Princess Celestia's death was unexpected. Twilight Sparkle was just in the process of sending a letter to her mentor inquiring why this morning’s sunrise was seven minutes late, when Spike burped a letter from Luna instead.

That's strange, Twilight thought as she bit the top of her quill. Princess Luna was not one to send letters. So far, since her transformation from Nightmare Moon, she had sent a total of two—both RSVPs. I wonder what's happened. Twilight unrolled the scroll.

Dear Twilight,

My sister died this morning. Get your friends and come to Canterlot at once!

Luna

Dead? Twilight's heart froze as her mind struggled with the concept. Princess Celestia can't die! Tears moved faster than logic, appearing in the corners of her eyes and sliding down her cheeks. She's immortal! Twilight stomped on the ground, startling Spike into the air. She's eternal! She stomped again, causing the entire room to tremble.

"Err, Twi?" Spike ventured tentatively, lifting a hand.

"She's supposed to last forever!" Twilight shouted. Her mane flickered with magic, her eyes glowing an incandescent white. "I must see her!” she whispered, clenching her jaw. With a flash, she popped out of her castle and straight into Celestia's throne room.

"Princess!" Twilight galloped into the main hall and up the staircase. "Princess Celestia!" Why aren't the guards here! It's their duty to protect their princess!

Twilight ran straight to Princess Celestia's bedchamber. Memories flashed before her eyes: the day the Princess made Twilight her student, the day she taught Twilight her first advanced spell, the day she sent Twilight to Ponyville. As far back as Twilight could remember, her mentor had been there for her, guiding her gently, and now she was—

"Princess!" Twilight burst into the bedroom.

"Great! Just great!" An extremely annoyed Luna turned around, glaring at Twilight. "Of course now you show up!" She snorted in discontent. "And alone. I thought I told you to bring your friends!"

"Princess Luna?" Twilight stopped in her tracks, wings extended. "What are you doing in Celestia's room?"

"I was trying to take things into my own hooves!" Luna diverted her attention back to Celestia's bed. "Until you barged in."

Twilight's left ear twitched. This was no way to mark the passing of a monarch, let alone her own sister. Wasn’t I supposed to come? The message was very explicit. And even if it wasn't, there was no way Twilight would remain in Ponyville, not when she knew Celestia had died. Quietly, she took a few steps forward. Could it be that this cold welcome was the way Luna dealt with grief? Despite the front she put on, the Princess of the Night was quite sensitive. Maybe I jumped to the wrong conclusion?

"Err, Princess?" Twilight approached slowly. "I—"

"Twilight!" A young filly jumped off the bed and flapped her way over to the mare. Pink mane, white coat, wings, and a horn... if Twilight didn't know any better, she'd swear she was looking at a baby alicorn. "My faiful student!" The filly squeaked with her high-pitched voice as she landed on the floor.

Confused, Twilight turned to Luna for advice, but only received a sigh in response.

"Where is my fwendship cake?" The filly hopped eagerly.

"Cake?" Twilight's eyes widened.

"Oh, for the last time, Tia, there is tons of cake in the kitchen." Luna didn't seem one bit pleased. "Just raise the sun, like a good filly, and we'll go have so—"

"No!" Tia pouted, moving under Twilight's wing. "I want fwiendship cake! And waising the sun is bowing."

"You're being unreasonable, Tia..." Luna grumbled.

"I am not! I'm the older sister, and you have to do what I say!"

Twilight blinked, then again. Her mouth opened, in an attempt to voice a question, yet only incoherent utterances came out. What in Equestria is going on? She looked down at the filly. She seemed a bit older than Flurry Heart, though just as rebellious. Her wings were far smaller in comparison, yet her cutie mark compensated—

"Huh?!" Twilight froze. The filly was too young for a cutie mark! What was more, this wasn't just any cutie mark, this was a mark Twilight—and the whole of Equestria for that matter—knew all too well. "Princess Celestia?!" The purple alicorn pulled back in shock.

"Yes, yes," Luna sighed, while filly Celestia looked at her with the smuggest of expressions. "She's Sis, alright. And she needs to get the sun up before noon!"

"But you told me the Princess died!" Twilight's head wobbled slightly. "You said in your letter that—"

"Yes, she did. And this is the result." Luna pointed a hoof accusingly, only to have the filly stick out her tongue. "Oh, will you act your age? I was never like this!"

"No!" Filly Celestia was adamant. "I am the older sister! You must wisten to me!"

"I... I don't understand..." Twilight's ears drooped down. I must be in a dream. No, in a nightmare! Surely this has to be a nightmare.

"Tia, if you raise the sun, Twilight promises to bake you a friendship cake," Luna said in a soft voice. The new approach seemed to have succeeded, for the filly's ears perked. As much as she tried to act calm and uninterested, those traitorous ears had turned towards her sister, like a pair of eagles targeting a trout. "There'll be strawberries," Luna tempted.

"Humph!" Filly Celestia glared at her sister. "You're so transparent, Woona! You know that, wight?" She looked at Twilight, then back at Luna again, narrowing her eyes. "The cake better be worth it!" She flew out of the window. Shortly after, morning came to Equestria.

What? How? Huh? Twilight stared blankly, frozen as a living statue. Her wings and ears were the only things moving, occasionally twitching, as her mind reset after each loop of internal questions. Luna, on the other hand, didn't seem worried one bit. On the contrary, she seemed somewhat relieved—albeit in an untypically grumpy fashion. Glancing at Twilight, she shook her head, then went on to remove a pile of golden toys from the bed, levitating them to the opposite side of the room.

"Don't worry," Luna said, arranging the toys neatly in the cupboard. "She's already forgotten the conversation. Most probably she's off chasing butterflies or something."

"But that... that's..." Twilight stuttered.

"I know," Luna sighed deeply. "Honestly, I swear each death is worse than the last. It's almost as if she's doing this on purpose. Took me over an hour to get her to stop flying around the room like crazy. I barely had the time to write you a letter."

"But she's..." Twilight pointed at the window. "She's Celestia! The great, eternal, wise..."

"I wouldn't go that far." Luna narrowed her eyes. A moment later she paused, looking at Twilight expectantly. "Let me guess, Tia never had this conversation with you?" She shook her head with a sharp tsk. "Typical. Leave me to do the dirty work, just like last time."

"But she..." Twilight started again, but a hoof on the muzzle quickly make her stop.

"Listen, Twilight. Maybe it would be better if you sat down," Luna suggested.

Sit down? Twilight thought. As if that would help anything! It's not like sitting down would explain how a filly Celestia just appeared, and everypony seems to consider it normal! Well, not everypony, since none of them are here, but still! Nonetheless she obeyed, sitting down on the floor, wings closed.

"Tell me, do you think alicorns are immortal?" Luna glanced briefly out of the window

"Uh-huh," Twilight replied, still uncertain what to make of things. According to her research, Celestia and Luna were as old as time itself. There was some ambiguity regarding her own nature, as well as that of Cadence, but it was a pretty safe bet that they too had been granted longevity, if nothing else.

"And do you know what eternity is?" Luna deliberately avoided looking her in the eye, continuing to stare aimlessly outside.

The younger alicorn didn't hesitate. "It's the moment from the beginning to the end of time."

"Yes. A very long time. Enough for any creature to become insane."

"Like Discord?" Twilight couldn't keep herself from saying. For some reason, each time someone asked her a question, she felt like she was back in school again, eager to make a good impression.

"Snrk!" Luna tried to stifle a chuckle. "Yes, like him." She looked over her shoulder. "The chaos is his mechanism to cope with eternity. Alicorns, much like phoenixes, have found a different approach."

"You mean...?" Twilight gasped. Alicorns die and are reborn? This is astonishing! I must find out more on the subject!

"Emotions are what keep an alicorn going," Luna continued. "That's why we value our ponies so much. They give us a reason to live. Celestia treats them as her children, looking over them, helping them grow, assisting when necessary. You yourself had made her life bearable this last decade." Twilight couldn't help but smile at those words. "But even so, emotions fade away with time, and Tia had been alive for over a thousand years. When the last trace of emotion is gone, for a single moment we revert to our pure essence and are reborn as fillies, our emotions recharged."

"So this Celestia is an entirely different Celestia?" Twilight tilted her head, coming to the most logical conclusion.

"No. She is the same Tia, you and I knew." Luna laughed. "She has all her memories, her skills, her knowledge. The only difference is that she is a filly, and as a filly she is prone to mischief. And she's also very touchy."

"Touchy?" I don't like the sound of that.

"Quite." Luna frowned, moving away from the window. "Do you remember what my appearance was after you freed me from my Nightmarish state?"

"Err, yes?" Twilight closed her eyes for a moment. Come to think about it, Luna had seemed somewhat younger after their battle.

"That's because I had died a few days earlier... well, a thousand years and a few days earlier." She winced as she said it. "One of the problems with being reborn is that we tend to be overly emotional, as you've seen with Tia here. At the time I was upset that more ponies liked her than me. Tia told me to grow up."

"What?!" Twilight jumped to her hooves. "You mean the entire reason for the Luna-Celestia divide, your banishment to the moon, and all relating consequences, was that?! You being upset at your sister?!"

"I was quite emotional at the time!" Luna looked away, her cheeks flustered with shame. "And it's not like Tia helped! She could have just lied, you know! It would have been over in a few weeks. She chose to yell at me, so I did the only thing I could think of."

"Try to take over Equestria and curse it to a sunless existence?" Twilight arched a brow.

"I never said it was a good idea!" Luna pouted. "Emotions make a pony stupid. That's why I called you. I was hoping you'd put some sense into my sister, especially in her current state. You won't believe what I had to live through last time she died. It's a miracle I kept my wings intact!"

"Right! Fine!" Twilight grumbled. I can't believe I felt so sad and scared about this. I can't believe Princess Celestia never told me about any of it! Now I'm supposed to babysit my mentor? She shivered at the thought. "Err, how long will she remain a filly? Not a thousand years, I hope?"

"Pfft, of course not." Luna waved a hoof. "A few weeks at most. Possibly a month. No more than two. You can never tell with Tia; she seems to enjoy being a foal. I usually try to speed through this traumatic experience as quickly as possible."

"Two... months." Twilight's wings and ears drooped down. "I'm supposed to babysit Princess Celestia for two months?"

"Oh, stop worrying, Twilight Sparkle." Luna smirked. "I have done it many times before. There's absolutely nothing to worry ab—" The sun outside vanished, plunging Equestria into darkness once more. "—out." The Princess of the Night looked at the ceiling, innocently.

"I must send a letter to Spike." Twilight summoned a quill and some parchment. These are going to be two long months.