Cadence could not help but feel that her husband was abusing his connections as a Prince of the Crystal Empire.

Who was she kidding? His actions were downright out of line.

What kind of brother employs a number of royal spies to secretly observe his little sister as opposed to the enemies of the kingdom, each one tasked in recording her daily routine in great and somewhat terrifying detail for his intense scrutiny?

It was at this particular juncture that Cadence thought it was right to intervene before it inevitably crashed down around him.

I understand he loves her dearly and would do anything to protect her, but, I think he is going a little bit too far just to find out something he could simply ask her.

It’s kind of embarrassing… and what is worse? He won’t even admit it… however, I know exactly what the problem is here. He’s afraid his little sister has finally met her special somepony and is doing…

Cadence blushed at the thought as she calmly walked through the halls of Canterlot Castle.

Well. She’s a grown mare now, so, I don’t see what the problem is if she is exploring herself with others. But, I suppose I will soon find out the truth from the mare herself. A little bit of girl talk between sister-in-laws will clear this all up and I can finally settle his mind…

Or unsettle it, if it is indeed a stallion.

Twilight Sparkle had been acting very strange since she ascended as a Princess. She had all but cut ties with her brother and even refused to join Princess Celestia and Luna on visits to the Empire, which prompted many sleepless nights for the Prince because he just couldn’t stand the notion that his little sister might have found another stallion to depend upon.

Cadence could not help but think it kind of cute. If anything, his concern (although excessive at this point) only deepened the love for her husband. He was too kind and caring for his own good, at times.

That and he’s a rather big crybaby, Cadence added as an endearing afterthought.

The two siblings only recent mode of contact was the weekly exchange of letters and even then, they were short and to the point.

Upon arriving at the entrance to Twilight’s chambers, Cadence knocked and waited for several minutes. Hearing no response, Cadence repeated the action a few more times before resorting to interrupting a passing guard, inquiring as to the whereabouts of her sister-in-law.

Discovering the mare was preoccupied in the library, a sudden and rather dangerous idea came to her.

Twilight Sparkle used to keep a detailed record of her thoughts and actions throughout the day…

A diary of sorts. If there was ever a place to search for the answer, it would be there.

Cadence infiltrated her sister-in-law’s bedroom all for him, and to be perfectly honest, she felt more than a little bit guilty for what she was doing.

But she had to know the uncensored truth.

After all, Cadence had promised him.

Only love could change a mare so suddenly, Cadence thought as she glanced under the mare’s bed, smiling as she noted a plain white book hidden away towards the back.

The discovery of Twilight’s diary had prompted Cadence to lock the bedroom door magically, just in case somepony happened upon her trespass.

Content that she was safe for the moment from any surprises, Cadence took the diary and headed over to the bedside cabinet, placing the book upon it as she flicked through to the latest entries penned on the crisp and clean pages.

Bizarrely, some of them were stuck together.

Glue? It’s not like Twilight to be this messy or reckless with her books.

Cadence sniffed the air.

It kind of smells strangely musky though… like Shining.

Pushing the thought from her mind, Cadence carefully parted the stuck pages to reveal a rather large entry.

Ah ha, here it is. Her most recent entry… huh? The writing looks quite rushed. This is far from the neatness I am normally used to from Twilight’s letters.

I don’t know what happened to me since becoming a Princess, but I have grown very fond of the addition to my anatomy.

Addition? Cadence blinked, clearly confused by the comment.

Before, whenever I felt turned on by anything, I simply yearned for something to fill me. A hoof… my toy. Once I achieved my orgasm, everything felt… great… resolute… blissful, you know?

I felt satisfied.

Oh… I… I shouldn’t be reading this… Clearly affected, Cadence blushed, though continued to read regardless.

But not anymore.

This is something different.

Since becoming a Princess, no matter how many times I release my tension, I just want more.

Is this what stallions feel? The overwhelming urge to feel something hot and moist around them constantly? Desperate to experience the sudden buildup of pressure that with each stroke erupts into a frenzy, as they work to achieve that heart-stopping, silent scream as they ejaculate their hot semen inside of their lovers…

Cadence quickly stole a glance to the door. “Twilight… this is… this is, so…”

...the mind numbing sensation followed by the shattering rush of something rushing out of you, seeking to smother whatever surface it can… to impregnate…

Before the concept of pregnancy somewhat scared me and yet now? The idea of… cumming inside of another mare without protection—the concept, it’s just so thrilling to think about!

As time goes on, my every waking thought has been to satisfy the sleeping, lusty monster inside of me… and I can’t stop touching myself whenever I think about it.

I can’t stop making myself cum.

Cadence was flabberghasted. She was not entirely sure if she wanted to read any more.

I used to masturbate maybe once a week to relieve the stress of my duties, but now I can’t stop. Everyday-no, every morning and every evening! Whenever I am alone and I get the chance I have to jerk one out.

What’s worse? I can’t stop thinking of her.

Her? Cadence swallowed hard.

I… I need her.

No... I don’t need her.

I must have her.

I want to cum in her… with her… on her face… on her flank—in her flank! On her tongue—her lips—in and on every part of her! I want her covered in my semen and begging for more as I masturbate into her gaping mouth!

Cadence took a few steps back, her eyes still locked upon the dairy, shocked to the core as almost every part of her told her to turn around and trot away… and yet, there was one small part of her that wanted to know more.

A small part of her was perversely interested in the inner most secrets of a mare she once thought pure and innocent.

Returning to hovering her gaze above the dairy, Cadence turned the page hesitantly.

Just thinking about her as I write these words… I’m hard already.

I need something to fuck.

I want to fuck her with my cock and make her scream!

Cadence quickly tore herself away from the bedside cabinet as if the furniture had caught fire, blushing red and utterly at a loss for words as she retreated, unable to read anymore of the smut or be anywhere in its vicinity.

“C-cum inside? W-what? Who?” A bigger question lingered at the forefront of that list and it was one that confused her exceptionally. “... already hard? B-but… that…”

How? Twilight’s a mare… she doesn't have the… thing, to—

The bedroom door handle’s sudden movement caused Cadence to whirl about and stare wide eyed in a panic, momentarily forgetting she was trespassing uninvited. She was glad she had locked the door upon entering because the voice on the other side caused Cadence’s hairs to stand up on end.

“Huh… I don’t remember locking the door.” A long suffering sigh huffed from the owner of the voice. “Don’t tell me it’s jammed again. I really need to ask somepony to get this fixed.”

Oh, no... it’s Twilight! I got to hide!

Searching the room desperately, Cadence brought her gaze to the closet and quickly dashed on over to it without thinking.

She hadn’t a moment to lose. Twilight could teleport herself in at any moment! She had to hide herself and she had to do it fast!

Throwing open the closet with her magic, Cadence’s eye twitched as she gazed upon the space normally reserved for clothes, which she had figured she would easily hide herself amongst.

Instead, the space was stacked head-high with dusty old books.

For the love of… Cadence complained internally, though wasted little time in stuffing herself into the dusty, cramped space in-between the stacks of reading material.

Next, Cadence used her magic to carefully close the closet just as a flash of lavender bled through a slight crack in the doors.

Okay, Cadence. Just breathe slowly and don’t move. It’s far too early for her to go to bed so just wait until she leaves, then open the window and just fly out—

Cadence immediately cursed herself.

Why didn’t I do that in the first place?! Urgh… now I’m stuck here! What a fine mess you've gotten me into, Shining! The things I do for you...

But then again, what did she discover that she could tell Shining Armor, anyway?

Nothing, that’s what!

Cadence was fully not prepared to share his little sister’s most intimate and surprisingly erotic thoughts, especially if they were that… vulgar and… detailed...

Not to mention his little sister was thinking of a particular mare rather than a stallion.

I never knew she swung that way… I always thought of her as the studious, married to her work type… I figured Flash Sentry was more of her thing if she ever wanted to pursue a relationship… but then again, he is kind of a mess.

“Well, I suppose it saves me locking the door.”

Twilight’s voice broke Cadence out of her thoughts, causing the Crystal Princess to bring an eye close to the crack in the door which happened to afford a perfect view of the foot of Twilight’s bed.

Cadence silently observed as she watched Twilight Sparkle walk into view and sit at her bed, stroking her…

WHAAAAAAAAAAAAT?!

Aghast, Cadence drew her gaze away and clamped her hooves over her lips to prevent the yelp of surprise from spilling out of her.

How is this possible? I would have noticed something like this when she was a filly! And I am pretty sure this is something Shining would have warned me about way in advance! This is… this has to be some kind of dream...

Right?

Leaning forward to peer out of the closet once again, Cadence observed as Twilight laid at the foot of her bed, stroking the long phallus that protruded between her rear legs.

“C-cum…” She could Twilight whisper hotly to her lonesome self.

It’s… it’s massive. Bigger than—

No! This is not something to think about… this is your sister-in-law and she’s… your brother-in-law? I don’t understand this situation.

Just what in Equestria is going on here?!

Swallowing hard, Cadence quietly shifted in the confined space, her erect wings making things very awkward to maneuver without drawing suspicion towards her hiding place.

Twilight was going to town on herself. There was no desire behind the strokes that caused the young Princess to writhe and pant upon the bed. Her strokes were so quick and desperate that Cadence could almost imagine that the mare was trying to rip the appendage off from the root.

“Ahhhn~mpnh!”

Cadence observed as the mare arched herself forward and plunged the tip of her own penis into her mouth and began to suck noisily.

This… this is… just… impossible…

“Mmmnnph~” Slurp. “C-Cadence… suck me…”

Wait… w-what?

Cadence pushed an eye closer to the gap as her name was mentioned.

“Y-yes… harder… f-fuck, me… ah… ahnnn! I’m c-cum—”

Blushing hard, Cadence glanced back at her wings, cursing their current erect state.

This has to be a dream. Some kind of, weird, Discord influenced dream!

She wrinkled her nose.

“ACHOO!”

Cadence froze, feeling the blood drain away from her face as she thoughtlessly released a sneeze she wasn’t expecting.

Quickly she pulled back from the gap, covering her muzzle with her hooves.

Crapcrapcrapcrap!

“H-hello?” Came Twilight’s cautious tone. “I-Is somepony in there?”

“Oh, no…” Cadence whispered as the doors to the closet slowly opened, revealing Twilight Sparkle standing with both of her eyebrows raised in shock at just who was hiding in her closet.

“C-Cadence?” Twilight asked incredulously. “Why are you in my closet? How long have you… um, been there?”

“OH!” Cadence smiled nervously, laughing while she struggled to keep her eyes away from the large cock hanging from underneath Twilight’s body. “Funny story, I was… experimenting with a teleportation spell and I just so happened to appear here! Funny, right?”

Twilight Sparkle blinked. “You accidentally teleported halfway across Equestria into my closet? That seems rather specific.” She raised her eyebrow.

“Y-yeah! Funny that! Heh… Oh well! I best be off and try and work out the kinki—I mean figure out what went long—wrong!” Cadence removed herself from the closet and moved past Twilight Sparkle, clearly embarrassed and heading straight for the door.

Upon attempting to depart, Cadence found herself trapped.

She had forgotten she had locked the door.

In her panic, she quickly turned from the door and made her way towards the window, only to be stopped by Twilight Sparkle. The younger alicorn blocked her path, looking very suspicious and yet, if her reddened cheeks were to be believed, easily as embarrassed as Cadence was.

“You heard, didn’t you? You… you saw?” Twilight narrowed her eyes.

“Oh, I… uh… saw nothing?” Cadence faked a smile, struggling to look at the younger mare in the eyes and not the thing that kept grabbing her attention.

Twilight sighed. “I can see you looking at it…”

“Twilight, listen, I don’t know what I saw and to be perfectly honest? I think this is just some kind of dream that I need to wake up from badly, so, if you will excuse me, I will be leaving now.”

Stepping around Twilight, Cadence made yet another attempt to escape, and was intercepted again by Twilight Sparkle.

“You enjoyed it.” Twilight pointed a hoof to Cadence’s still erect wings. “Didn’t you?”

“I… I didn’t! I am just shocked that I would dream something so… something so—”

“Erotic?” Twilight finished with a gentle and somewhat sultry tone of voice that caused Cadence to blush again.

“Well, yes but I—”

Immediately Cadence was cut short by a needy and intrusive kiss that crashed against her lips, causing her to yelp and retreat in an attempt to flee. However, Twilight had locked her forelegs around the older mare’s neck and kept the kiss firmly in place.

A tongue invaded her mouth and she could do nothing to stop it.

Eventually, Princess Cadence ripped herself from the kiss by pushing her hooves against Twilight’s muzzle, her heart pounding against her chest as she breathlessly spoke. "T-Twilight! What i-in Equestria are you doing?!"

"If this is a dream, then it doesn’t matter what happens, right? Even if we kiss, even if we have… sex."

“S-sex?” Cadence stammered. “But… this isn’t right! Even if this is a dream... This is… I have to wake up. I don’t want to have sex with you, even in my dreams!”

Twilight shuddered in anticipation at the word coming from the other mare’s lips, even if it brought rejection along with it. "I don’t care... I want to feel my c-cock inside of you... I want your warmth to consume it. I want... I want us. So badly... So much so that it is driving me insane! It feels like something is building up inside of me and it is just begging for me to let it out... to let it, all, out..." Twilight's sultry eyes narrowed upon Cadence's lips. "All, over..." She added as a lustful afterthought.

"But I love your brother; we're married! I'm your sister-in-law! There's no way I can… I just don’t feel that—" The sudden presence of Twilight’s body pressing up against her caused Cadence to shiver and take a sudden step back as something wet and hot poked her side.

She knew what it was and dared not to look down.

"He doesn't need to know. Nopony needs to know, Cadence. If this is indeed a dream then I never want us to wake up." Twilight pursued, closing the gap. “You watched, didn't you? You watched me masturbate just now. You were intrigued, weren't you? Why else did you hide in the closet like that for so long without saying a word? You were excited, right? Like how excited I am right about now, right?”

"I-I don't know..." Cadence averted her gaze. "I... I'm not quite sure... I thought you were... I came here because Shining told me you were acting strange around him lately. You've been quite cold towards him and myself the last couple of weeks, but I never thought that it was because—"

"—your sister-in-law was masturbating to the thought of plunging her long, hard, cock inside of your flank?” Twilight interjected in a seductive groan, “I've been avoiding him because I almost can't control myself, anymore. I’ve wanted to say something since the wedding about my feelings but… but... but now I don't care. I will make you mine and I don't care what you say or what my brother thinks of me… I’ve always had this feeling for you since I was a young filly… I didn’t understand my feelings at the time but, ever since you married my brother and I became a Princess, I... I want to hear you scream my name… I want you to beg for me to stop as I make love to you... I love you and I want to show you just how much."

“Twilight, you can’t… I don’t like you in that way.”

Twilight’s pleading voice became desperate. “Please, let me show you. Just this once?”

Cadence pressed her back against the bedroom door, forcing her to rip her wide-eyed gaze away from the large, throbbing cock hanging below Twilight Sparkle. “N-no… I would never… Twilight, this is wrong. We’re family! You’re my step-sister and I could never love you like I do Shining Armor. I would never betray him to anypony… and… this is just wrong! I’ve known you since you were a filly and I just can’t do this! Please, control yourself.”

“I-I know. I know you would never feel the same way but yet, I just have to try, you know?” Twilight took a step back, tears forming in her eyes, her wings drooping towards the ground. “Cadence, you’re… not even curious…? How good I can make you feel?”

“Twilight,” Cadence reaffirmed in a stronger tone, narrowing her eyes upon the younger Princess with an air of authority, “I’m sorry, but I can’t. I’m leaving.”

Cadence barely looked at Twilight as she brushed past her, heading for the window so she could depart from the bedroom. “Don’t worry. I won’t tell Shining about this… it’d break his heart to know his little sister was thinking about taking away the mare he loves.”

“W-wait…”

Twilight’s trembling voice caused Cadence’s steps to pause. Turning, she looked back at the younger Princess with a slight frown, though tried her best to not appear as annoyed or as uncomfortable as she felt.

“Yes—wha?!” Cadence was met with a flash of light that momentarily dazed the mare, causing her to sway and fall back onto her flank.

Confused and blinded, Cadence drew her hooves to her closed eyelids, pressing tight against them as the strange fuzz bled throughout the rest of her body, spanning from the tip of her horn down throughout the rest of her body.

“Cadence… are you okay?” Twilight enquired, concerned.

Rubbing at her eyes, Cadence opened them, her stunned state boiling into anger as she realized what had just happened. “Twilight! How could you? You attacked me!”

“I’m sorry but there was no other way I could think of to fix this!”

“What do you mean? Fix what?” As Cadence’s vision cleared, her heart felt as if it had stopped the moment Twilight Sparkle’s concerned face came into view.

A wave of emotion crashed through Cadence’s body, causing the mare to tremble and gasp, forcing her to push her hooves to her lips to contain the noise.

The very image of Twilight Sparkle had caused her body to react in quite the unexpected manner. For her previous turmoil of betrayal was instantly replaced with an awe and wonder that felt unnatural.

“T-Twilight…” Cadence whispered softly as she slowly got back to her hooves. “W-what have you done to me?”

“I-I’m sorry, Cadence, I just—”

“Why… why do I feel… I want it?” Cadence groaned as her eyes slowly dropped to Twilight’s cock, shivering as she approached it, her mind screaming for her body to stop but to no avail.

Cadence’s head drooped low as her lips parted, breathlessly whispering her words the closer she got to the glistening tip of her sudden and unexpected desire. “I-I need it.”

Parting her lips, Cadence felt her tongue flattening as she slid Twilight’s long throbbing penis into her mouth and down her throat.

Author's Note

This story has MegatronsPen's seal of disapproval.

(Re-Edited for better clarity... because I can.)