Celestia's guard entered her study after a quick knock. “Twilight Sparkle and... guest, your highness. She says it's urgent.”

“Send her in immediately, then no interruptions until I say, excepting matters of life and death.”

The guard gave her a quick nod of acknowledgement, then exited. Twilight Sparkle entered, looking even more drawn than a few minutes ago, followed by a floating, bound and gagged dragon wrapped in a purple glow. A quick spell from Celestia closed and locked the door behind them.

“How?” she asked. “My best guards and protective spells are set upon your quarters and laboratories.”

“Trixie can apparently teleport enough mass to get a small dragon past your guards,” Twilight explained, her voice devoid of all intonation. “Teleport him into a storage area unprotected by spells, but connected by a series of air vents too small for any pony to crawl through.”

Celestia closed her eyes. “How much does he know?”

“Enough,” Twilight said in that same dead voice. “He knows that alicorn lifespans have changed since your and Luna's ascension.”

Celestia looked at her with obvious concern, disturbed by Twilight's complete lack of expression, but had to ask, “You took precautions, I'm sure.”

“My copy of the alicorn records are encrypted, using my own personal key. That's a key only I and my 'number one assistant' know. Of course as soon as he saw something encrypted, he must have concentrated on that as the most important. And he's always been good with those.”

Celestia shook her head. “This was not your fault, Twilight. You did everything reasonable, and then some.” The first expression Twilight had shown, relief, flashed over her face, but too briefly for Celestia's comfort. “Release him.”

The gag and ropes disappeared back into the nothingness they'd been summoned from, leaving a very unhappy dragon behind.

“Spike,” Celestia started. “Let me explain.”

“Sure,” Spike literally hissed. “Explain. Lie to me again.” His claws curled in rage, and Celestia wondered if she'd actually have to defend herself.

“No, Spike. No more lies.”

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

One month ago, in Celestia's private chambers...

“I suppose I should start at the beginning. First of all, you see, our sun died millions of years before ponies as we know them were born.”

To Celestia's surprise, Twilight didn't try to interrupt again. Celestia continued, “Our sun is what we call a white dwarf, cooling slowly. It's like... the dead body of a live star, glowing only from the heat it once had. Our earth was moved closer to it by the former inhabitants of this world before they lifted our ancestors into sapience.

“Lyra Heartstrings was right all along, in essence if not in detail. This world belonged to man, though she would not recognize them as they are now. They merged themselves with machines made of light, the legends say, and left for the stars. Before they left, though, they gifted our ancestors with intelligence and magic. You should realize that a lot of what I say about them is speculation, and all of it is sketchy at best, but I gather that they almost destroyed themselves several times, through their own drives. I think they wanted to give a more social, more naturally content species a chance, but unfortunately that may have hindered us as well.

“White dwarf stars cool very gently, but they do cool. After maybe a million years we'd progressed very slowly, and some 40,000 years ago our entire world was cold and dying, not just some region ponies migrated from as in Hearth's Warming Eve tales. It was a desperate time, and they did something very desperate indeed. You know from experience that cutie marks, and destinies themselves, can be altered, but I think you still don't know how much.

“Seven hundred unicorns they tried to change, not switching marks between friends but trying to come up with the destiny they desired. Five hundred and twenty-four died, some in agony.” Celestia shuddered. “For the spell, they had to be too young to have cutie marks of their own. Many of them were newborn foals.

“The rest, all but two, went mad. One of the two can keep the sun alive indefinitely. One can keep the sun alive for centuries, if need be, and beyond that... Beyond that, we don't know. The sacrifice of the initial foals, I think, is why the Hearth's Warming Eve tales speak of the unicorns raising the sun and moon. How many of that tribe know the truth to this day, I cannot say.”

Celestia raised an eyebrow at Twilight, and her student understood that questions were welcome. “The two. You? And Luna?”

“Indeed. We are sisters not in blood, but in origin... and in damnation. We do not raise the sun or moon, as is commonly thought. I sustain it, and Luna's 'stars' are her training to do so in case I fail.”

“And that gave you immortality?”

Celestia closed her eyes, and her voice was a whisper. “Not exactly.”

“I don't understand.”

“And I wish you didn't have to. Every century a few alicorns come into being, usually from unicorn stock, sometimes with the aid of myself and a select few scholars from each tribe. How isn't important right now, but we can do it only rarely. Beings that should live as long as an Earth pony, unicorn, and pegasus combined. The records you sought would have shown such lifespans before our rule. But now each ages quickly, living only as long as their birth tribe gave them.” Her eyes caught Twilight's. “And Luna and I live a while longer.”

In a space of seconds Celestia could see in Twilight's face: the realization, the refusal of it, and then, finally, acceptance. “You...”

“The same thing that made us alicorns and gave us the power to preserve life itself lets us tap the years other alicorns would have. Should have. They keep me alive to light the day, and they keep Luna alive in case she is needed.

“That is why Luna fled when the changelings invaded. Even if Canterlot fell, even if I died, she had to survive. If not for my little ponies, then for everything else.”

“How many?” Twilight asked through growing tears.

Celestia understood, and let go a great sigh before her horn glowed, filling the large room with golden ponies in miniature. “One thousand, one hundred, and seventy-two.” Her own tears fell now. “I brighten the sun a little at their ascension, and dim it as we have claimed them. One thousand, one hundred, and seventy-two graves filled early so that Luna and I could live.” She paused as her voice cracked again. “I remember them all, Twilight. Sky Skimmer. Bubble Champion. Silk Splendor. Good Gravy. Tiffany Glass. Square Deal. Gilded Lily. Ebony. Sweet Delight. Star Stalker...” She made a small choking sound, and had to stop.

Twilight knew, but didn't know how she knew. “That one with the Night Guard wings?”

Celestia nodded. “Star Stalker. His special gift was the night – not it's creation, but simply living and delighting in it. Ostracized for not looking like other pegasi, he grew to be perhaps the noblest soul I have ever known. One thousand years ago, Luna would have given up everything – and unlike almost every time somepony says that, I mean, literally, everything -- to spend one lifetime with him. Now she reshapes her pegasus guards into his image. I think she has at last forgiven him his sacrifice.”

“Then Nightmare Moon...?”

“Your perceptiveness does you credit. Remember what I wrote you when you mentioned a mare filled with jealousy that everypony ignored her night? 'Old mares' tales,' I said, and they were. But behind many legends, you'll find a kernel of truth. She would indeed have brought about eternal night, eventually, for that one love, and then in a blind quest for revenge and release if you had not restored her sanity. She and I would have lived a few more decades, and died, and thousands of years later the sun would have again been too cold to sustain life.

“I told myself that I wanted you to have a few years without the weight of this upon you.” Celestia's voice briefly hardened in anger, directed at herself. “But that wasn't it. It was a selfish lie I told myself to salve my conscience.” The anger evaporated as quickly as it came. “The truth was, I wanted a few more years before you hated me.”

Twilight sobbed silently, not knowing what to say.

Celestia turned away, and as she continued each word felt like a nail in the coffin holding whatever love Twilight could have ever had for her. “It's true that they would all have died eventually, but that's true for every victim of every murder. And if we died, Luna and I, if we went to whatever ill welcome we no doubt richly deserve, then our victims would still die, along with everyone else in the eventual long dark that came. And it would cost far more lives to create new avatars for the sun than we claim. 40,000 years, and we have yet to find a better way. Even Discord cannot help, though I feel he would, in this, if he were able. It is too contrary to his nature, and it seems even nearly omnipotent avatars have limits according to their natures.”

“And Cadance?” Twilight asked, bringing another note of pride to her mentor's heart as even now one of her first thoughts was for another.

“She will have a unicorn's lifetime, Twilight. She knows. I actually think it's a comfort for her, in a way, now that she's married to your brother.”

“Is this why Luna reacted so strongly to Nightmare Night?”

“The night where the Mare in the Moon devours ponies? Its existence is a coincidence, I think, but no doubt one that hit too close to home, especially as, in a way, she had wanted to stop a thousand years ago, and I forced it to go on.”

“And on and on until...?”

Celestia turned back, her expression for once not of anguish, or at least not pure anguish untempered by some trace of hope. “You're the most promising thing to ever happen to us, Twilight Sparkle. And that the Elements responded to you was, I think, a positive sign indeed. Maybe you can find a way to create another solar alicorn without the hideous cost of my creation, so that we can live our natural lifespans. Maybe you can find a way to keep the sun alive through a general spell that any unicorn could cast, or a group of them. A way to perform an age spell without having been thoroughly corrupted by an amulet first. A way to create alicorns faster, so we'd only have to take a few days from each. A way to take a few seconds from everypony, not just alicorns. Something we haven't even thought of yet.

“Make no mistake. I fear death, even after all these years. I simply fear more the cost of my continuing to live. I hope you will be my salvation. Our salvation, for Luna feels as guilty as I. And I hope that, some day, you'll forgive me.”

Twilight smiled bravely. “You're giving yourself too little credit, your highness. You're not taking from me anything you haven't first given.”

Celestia's expression darkened, and the predatory nature of the step she took toward Twilight sent a shiver through the younger mare. “You're young yet, my faithful student.” Celestia's tone was suddenly menacing. “When the years creep up on you, when every step eventually brings pain, when your wonderful mind begins to fail you at last and, for a while, you know it? What then?

Celestia took another step forward, and Twilight a half step back. “And what if I find a way to take advantage of dragons? If I give Spike another thousand years...” Another step forward. “And then take them away for myself? What would you do then?”

Twilight was shaking her head, silently mouthing denials as she ran out of room to back up.

Celestia still had room for another step forward, bringing her face to face with Twilight. Every word now landed like a blow. “Do you think it was coincidence that you hatched him? He's now connected through you. An alicorn. Now with an alicorn's magic.”

“No!” screamed Twilight in a voice that echoed through the room, a flare of magic hurtling Celestia back. Twilight was half aghast at her own actions, but found herself bracing for a fight. Celestia, though, when she found her footing, just chuckled ruefully.

“I see you've found the Royal Canterlot voice. Twilight, Spike is safe,” Celestia said. “I had hoped, once, to use dragons, since it would hurt them far less, and there are many more dragons than alicorns. A few years from each would scarcely be missed, like a day from one of us. Spike's father, if he deserves that title, sold us the egg. It's purchase for my research was one of many foul compromises I've made, for all that it did seem safer with us than with 'family.'” She looked again into Twilight's eyes. “It didn't work, even after you hatched Spike's egg. I only tried to take a few seconds, I swear to you. And I apologize – yet again – for scaring you, but I had to made you understand what it would feel like to the next of kin. This is why we keep this secret. Imagine if it were Sweetie Bell? Or Apple Bloom, for some few, fortunate alicorns do come from earth pony stock.”

“Princess or not, Applejack would buck you into next week.”

Celestia chuckled again, this time with a little genuine mirth. “She would at that. But your friends and their kin are safe. Not, alas, from compassion's sake, though I wish I could say that was so, but from caution's. Too many ponies familiar with too many cases might arise if we preyed from the same area too frequently.”

“I'm glad,” Twilight quietly decided.

Celestia nodded knowingly. “And that, in essence, is why, no matter how much forgiveness we receive, we are guilty.”

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

The present day, one wall of text later

“Do it,” Spike insisted. “I wouldn't miss a century.”

“I can only take from alicorns, Spike.”

“Please! I... I can't be all alone for so long.”

“I'm sorry, Spike. I simply cannot.”

The dragon no longer glowered, but hid his face in his hands. “I hate you,” he insisted through his tears. “She may forgive you, but I swear I never will.” Celestia accepted the condemnation silently, head bowed.

Twilight, her face now filled with concern, approached him, “Spike...”

“No! You can't let her use you like this. She's killing you.”

“Spike, she's asking me to kill her.” This made him look at her, if only in confusion. “Spike, I found something, not anything solid and it probably won't work, but it might let us keep the sun alive ourselves. That would have meant no more need for a solar alicorn, and that would have meant that Celestia would have grown old and died like anypony else. She was happy at the possibility.”

Celestia nodded. “Two friends, each with a reluctant knife at the other's throat, talking politely over tea. It was almost perverse enough to be politics,” she mused, smiling weakly.

“Tea and cake.”

“Very good cake,” Celestia assured her.

Spike looked angrily at Twilight. “How can you be okay with this? Stop being okay with this!”

“Spike,” she answered gently. “A very wise pony once said, 'the most important thing isn't how much time we have together, but making our time together count.'”

Spike sniffled. “You're the one who said that.”

“And I was at my very best, wisdom-wise.”

Spike almost smiled, before realization hit him. “This is all my fault, isn't it? I mean, that you know. It's all my fault! If I hadn't asked you to check...”

“Spike, I would have...”

“No,” Celestia interrupted. “No more lies. Not to him. Not even the most comforting ones.” She turned toward Spike. “Yes, Spike, she learned earlier because of that. I don't know when I would have told her, otherwise; Luna had been berating me to do so since soon after the coronation. But realize this – her knowing earlier gives her more time to find a way out. She might be able to save herself, and untold future generations of her kind, and perhaps more. If you feel you must take the blame for a few years or so spoiled, though there's no way you could have known, then you should take credit as well.”

Spike glared at her. “'No more lies,' you said?”

“No more lies, not to you. I cannot let this go public, and regrettably I do lie to them when I must.”

This was Twilight's turn to re-insert herself into the conversation. “Spike, for me, please? I'm sorry I lied to you, but please trust me now, this has to be a secret from everyone.” She feared that if he didn't agree, Celestia would indeed have to have him exiled, put in a dungeon, or put in a dungeon in a place she exiled him to, if not sent to the moon.

“For you, Twilight.” He scowled again at Celestia before turning back to the purple mare. “Only for you.” He sighed, then, and looked a little sheepish before saying, “But let's say, for a completely random example, that Trixie and the girls thought you and Celestia had been replaced by changelings?”

“Ah. A completely random example that would have been completely randomly started by...?”

“Well, it made sense that they'd take you first if they could, since you had a spell that could reveal them, and then you wanted to get away from those who knew you best.”

“It's OK, Spike. Though I don't know how to prove to them that I'm not a changeling. Even if I zapped myself with my stun spell, they couldn't be sure I was giving myself the full zap.”

“I'll take care of it,” Celestia said. “I'll invite them to my next 'Raising of the Sun'. They'll believe me when I tell them that a changeling cannot manage such a feat.” I simply won't tell them that their beloved ruler cannot, either. It seems now I can only convey the truth itself by using another lie.

“And I'll have my number one assistant with me,” Twilight noted happily. “You can't deny me that now, Princess.”

“I have no desire to do so. Your little brother will need a security clearance so high that even its existence is itself a state secret. I'm looking forward to seeing the expression on my Minister of State's face.”

“And as for the library...” Twilight mused.

“Trixie files books under 'T' for 'Trixie wants to read this later,'” Spike noted.

Twilight actually paled. “We'll send another librarian, Spike, even before your move back here. You've suffered enough.”

Author's Note

There's Celestia's dark secret in full, though not the end of the story. Any mistakes in grammar are my own.

Any mistakes in astrophysics are because astrophysicists use carefully crafted mathematical models backed up by much research, rather than going through the much easier method of reading pony fics. You think such smart people would know better.