"Where... Where am I?" Wondered Prince Blueblood.
The last thing he remembered was... The Grand Galloping Gala.. And... That mare.
And now here he was, tied to a chair. Leather bonds held both sets of hooves to the arms and legs of the thing, unsightly and provincial as it was. Oh how the mighty have fallen, he thought with a grimace.
The room was dark, shadows covering the walls, the only light coming from a chandelier above his head. Craning his neck up, he could see the cutie mark of Princess Celestia in mosaic on the ceiling. It seemed he was in the palace someplace.
"Hello, 'your highness'," said a refined voice from somewhere in the shadows.
"Wh.. Who are you? Do you want ransom? You'll not see a penny from me!"
"Oh but your grace! I'd never dream of taking away your vast fortune!" The voice said mockingly, as it's owner stepped into the light. It was a white unicorn, purple mane, clearly a mare. In fact, if memory served...
Her name was Rarity or some such. That mare from last night! A gold digger, like the rest. He'd never find a mare who loved him for him, all they ever wanted was his money and status. He'd give them the run around, sleep with them and let them brag to all their friends about how they bedded the illustrious prince.
"N-Now Miss Rarity, let’s not do something we’ll regret…"
"Oh but your highness, I’m not gonna regret anything; I’ll enjoy every moment."
"What.. Do you want with me?" He asked, voice quivering.
Rarity laughed as her horn lit, "I want revenge."
She levitated something from out of a darkened corner of the room. It was... A.... Cake..?
It was small, simple, vanilla frosting messily applied. Clearly not expensive, and exactly what he expected a peasant mare like her to eat.
"You see," she continued, trotting over to where Blueblood sat, "I fully understand your fear of getting dirty, and have brought you here so we can get over it, together."
"And... And the cake..?" Blueblood asked, hoping she wasn't nearly as crazy as she sounded.
"Oh, I'm going to feed it to you!" She replied.
"What?" He deadpanned. What indeed?
"Well you see, the plan is, I'm going to feed you larger and larger, until you understand how much you humiliated me!"
As Blueblood opened his mouth to reply, the cake magically zoomed towards him, splattering all over his princely face.
"Buh-bluh-what?" He stuttered, incredulous.
Before he could utter a proper sentence, two things happened. One, Rarity winked at him. It was the most ominous wink ever wunk by ponykind. Two, the mess on Blueblood's face began to move. Crumbs, chunks of cake and frosting slid towards his shaking mouth.
"H--hgurrk!" He choked as the treat forced it's way down his gullet.
"Oh, prince! Are you choking? Do you need... A drink?" Rarity levitated a hose beside her as she stepped towards him. Blueblood tried to pull away, but the chair kept him firmly planted in place.
The cake was dry, terribly dry, crumbs coating his mouth and throat, and he couldn't deny that he could use a drink, but... Really?
Rarity shoved the hose past his lips, partway down his throat when his gag reflex kicked in. Delayed reaction much? He thought. Heaving to remove it, Rarity simply stroked his stomach.
"Oh don't you worry your handsome little head, auntie Rarity will have this all sorted out soon." Suddenly, the hose rocked to life. A cold liquid flooded his throat, down into his stomach.
"Do you like that? It's imported, just like you prefer all your food. From MossCow or some such place. I went there myself years ago. Oh, the sights, the art, the history!" She trailed off, theatrically describing Rushin' culture as Blueblood's stomach slowly filled up with milk.
Blueblood was incredibly uncomfortable, his insides freezing cold, a hose down his throat, and pressure building up. Slowly, he felt a bloating feeling as his trim, almost athletic belly developed a paunch. The tightening feeling was uncomfortable at first, but as he slowly grew, it began to ache, followed by a contracting wave of agony that shook his entire body.
"Ooohh, is Bluey-boy getting full?" Rarity cooed, stroking his growing belly. Big as a beach ball, he looked nine months pregnant already! Tight as a drum, Rarity caressed the ballooning belly, Blueblood groaning in pain.
"... And the ponies! Well, not ponies, cows! If that worker's revolution of theirs taught them anything, it's how to dress!"
It hurt! It hurt so much, the pressure, he was going to explode! He was a prince! A descendant of the great house Lipizzan! Seven times great nephew of Princess Celestia, he couldn't just burst!
The pressure in his stomach began to spread, Blueblood felt his flanks widen slightly from the fatty liquid pouring down his gullet. On his forelegs, he could see a bit of flab forming, and he could feel his chin tighten a little.
Pop! A dry sound not unlike what he was sure would happen to him, filled the room. It seemed... No, it couldn't, that only happened to mares, yet the evidence was right before him! His belly button had become an outie!
Suddenly, the flowing stopped! He look pregnant, at least triplets, his insides felt squished against the milk-filled ball of his stomach, his flank pressed against the edges of the chair.
"Is little princey full?" She cooed.
Blueblood nodded his head enthusiastically. Yes! He was full! He couldn't hold another drop!
"Then we'll have to move on to the next step in our therapy," she said, pulling the hose out of his throat. He greedily sucked down air as she carried off the object of his misery. Inside his stomach was... A rumble? Surely not out of place all things considered, but still rather distressing.
Bloorrghghhh...
Rarity was missing, hidden in the shadows around the edge of the room. With a sudden rock, he felt pressure building up again! In his throat, he could feel it, a tightness that could mean only one thing.
Uuurrrp!
The gas escaped his mouth and echoed around the room. It wasn't too surprising, his ballooned belly pressing against his guts, but Blueblood still shut his mouth quickly, a blush forming on his cheeks.
"Oh my! How unprincely!" Rarity chided as she stepped back into the light. She wasn't carrying anything, thankfully, but Blueblood still felt very afraid as she drew nearer.
"In fact, it fits perfectly with your personality! How can you claim to be a prince and treat me, a mare of class and quality, like some trollop picked up from the street?" Her expression darkened, and he could see the hate in her eyes, "Well, princeling? Answer me!"
He didn't want to answer. His lungs, compressed against his tight ball of a stomach, felt small and compressed. He could barely manage a whimper as he felt pressure coming on again. But this wasn't his throat, it was...
Fppprrt!
The gas sputtered, squeezing out from under his rump like air from a balloon who's end is being held tight. A rank smell, like an old pile of garbage, flooded the nostrils of both occupants. Blueblood's blush darkened as Rarity's eyes did the same.
ffffffrrrbbbbt!
"Now that's no way to treat a lady!" Rarity's mood suddenly shifted, from angry to the same unsettling cheeriness of before, "I think you need to be punished!"
"No, no no please! No more!" Blueblood found his voice, knowing deep down that pleading was useless, "I don't want to! No!"
Rarity ignored his pleas, instead choosing to light her horn and... Undo the restraints? The straps on his front and back hooves went slack; he lifted a hoof experimentally.
Suddenly, he was on all fours, running across the floor! His stomach jiggled painfully, the agony of each step comparable only to the pressure he felt building up in his throat again. He held it in, couldn't risk what Rarity would do to him if he--
Uuurrp!
He charged into the shadows, forcing his eyes to stay open even as childhood instinct told them to shut. He was finally free! He could escape! He could.... Oh dear. He was facing a wall. He danced on the spot as he swung his head around, looking for something, anything, to help him escape this nightmare!
The wall was, as far as he could tell in the darkness, completely bare and featureless. Not so much as a scratch on immaculate, almost regal white paint, he'd give it that.
A blue aura surround him as he floated into the air and was carried into the circle of light in the centre of the room. Rarity, visibly straining at the heavy load, deposited him before her.
"Did you really think I'd just let you go? You really must be as stupid as you look!" Rarity said angrily, pacing around the bloated prince, "I'm not finished yet! I'm just barely getting started!"
Blueblood tried to turn his head, but gasped suddenly as he felt the shock something cold touch his royal posterior.
Rarity shoved her face into Blueblood's bloated bottom, his butthole contracting with the caress of her tongue. A clean bottom, she thought happily, is the sign of a well-bred pony. His rear jiggled, the newly added chub quivering as Blueblood's entire body fairly shook with pleasure.
His cock, up till this point, had remained sheathed. No more. The tip slid out, the thick tube of meat growing until it reached the medial ring. How could anypony find this arousing? It was disgusting, he thought, that anypony could find this pleasurable. Sick twisted perverts that lurk in darkened alleys, only wanting their monstrous fetishes fulfilled by some unsuspecting mare or stallion.
Blueblood's body, however, had other thoughts on the matter. His belly, until now taught and firm, seemed to loosen as Rarity's tongue worked it's way in a circle around his puffy little anus. He could feel his flanks thickening, his rear cheeks puffing up, forcing Rarity to hold them open with her hooves.
He saw something moving in the dark, something long and serpentine. It's the snake, it's come to take me away! I've burst and I'm dead! His panicked thoughts were interrupted when he realized what it was. Held in Rarity's blue glow, the hose! Milk dripped from the end, a fact he barely registered as it flew back down his throat.
"Hrrk!" He choked. Rarity continued to work her magic, while her actual magic turned a tap in the darkness. The milk flow began almost at once, the fatty liquid forcing it's way down his throat, into his stomach. His thighs tightened, he could feel them growing. A butt like no other, he thought, trying to make the best of the situation, at least now I have the most spectacular Celestia-damned flank in Canterlot! Mares, stallions, all will want a piece! And from my ivory tower, I'll look down and whisper to the best and biggest, come hither.
His fancy words melted away, as he was lost in the joy, Rarity shoved her tongue right into his butthole, eliciting a groaning howl.
"Mrrrrrrhhh!" He cried around the tube. He could feel a drop of pre appear on his cock, almost lost amongst the feeling of growth, as his belly grew and grew. He was heavy, heavier than anypony he'd ever seen, his ass rounder than any other, the fat sagging downward and his dick throbbed in pleasure. It felt almost as if... Were his balls bigger?
Rarity, her tongue buried deep in the prince's anus, felt something touch her chin. Eyes tilted downwards, she saw Blueblood's princehood, fully erect, longer than any stallion she'd ever seen before. And above that, his testicles grew taught. Bigger and bigger, while his exercise ball-sized butt shook, his balls also became... Balls. Bally bally bally balls, filled with semen, growing to the size of cantaloupes before her very eyes!
They ached, oh how they ached, he wished Rarity would just get on with it and jerk him off or something, the pleasure not enough to cause release. He opened his eyes and drowsily glanced around. His legs were as thick as tree trunks, his cheeks jiggled as he tried to look down at them, around the hose still filling him with liquid calories. His belly surged, suddenly reaching the ground.
The feeling of the cold floor jolted him out of his ecstasy. Wait, what am I doing? No, I should be escaping! I'm a prince of Equestria, I can't be some big ball of lard!
He began to struggle, trying to move, his hooves lifting slightly off the floor. Blueblood flailed, words choking around the hose, Rarity was forced away by his shaking ass.
She was afforded a good view of her victim, fat and huge. Blueblood's belly, once flat and sporting the beginnings of a six-pack, was massive. It jiggled and wobbled, slightly tight against the skin, holding his hooves just inches above the floor. It stuck out between his thighs supporting his enormous, twenty-inch dick, a puddle of pre pooling on the floor around him.. His ass was huge, cheeks round as beach balls as they quivered, his cutie mark stretched out to cover the expanded mass.
His face, oh his face, he had two chins, and was slowly gaining a third as he struggled. Milk began to sputter around his bloated lips as he tried to force the tube out.
"Hrrrk--ptewie!" He spat it out, milk splattering across his face and the floor, unswallowed liquid draining from his mouth. He stared at his ruined body, tears welling up, and cried, "Why? Why must you do this to me!? Why?". His shaking stopped, his butt ceased jiggling, his belly lay still.
Rarity simply walked up to him, face to face, and took out a handkerchief. She wiped the milk off his puffy cheeks and mouth, licking the cloth as she put it away.
"If we had connected, if we could've been together, I would've done this anyway. Over the years, I would've fattened you up, turned you into the same fat mound of flesh you are now," she said, eyes glistening, "And now, now I've gone and done it and you'll have me locked up in a dungeon for the rest of my life. I'm so so sorry." She cried, hugging his head.
Blueblood could feel something welling up inside him, something he hadn't ever felt before, combined with an all-too common feeling.
"Miss Rarity," He said, "Look me in the eyes."
Rarity pulled back, staring at the prince's bloated face, then into his eyes. He reached out and gripped her forelegs with his hooves, entire body jiggling with the motion.
"Miss Rarity," he began, "I..."
He had spent his life a hedonistic brute, taking whatever and whomever he wanted and abandoning them when he lost interest, but now? He had finally found something to keep, or perhaps to keep him. All he knew was, they needed each other, and not just because the prince was completely immobile.
A mare, who turned from hating, and a prince, who turned to loving. In their hearts, they knew what they wanted, and they had finally gotten it. True love.
Suddenly, the feeling inside himself became clear, and he knew what to do. He pulled her close, her face before his, and locked lips with her. His bloated cheeks, his puffed out lips against hers, in that moment they each knew what they had wanted.

Blueblood's rear had it's own opinion.
Frrrrrrrrpppppt!

Author's Note

If you think this is strange and makes no sense, I'll point out that this is horrifying fetish clop and you shouldn't complain. I'm the guy running the storyline here, I'll do as I please.