“Twilight?” said Princess Celestia, surprise evident in her voice as her normally-unflappable demeanour started to show some fraying along its edges when she addressed her personal student. “What are you doing here?”

        For her part, the unicorn looked confused at the question and a pair of inquisitive mulberry eyes scanned the corridor quickly. “Am I not supposed to be here or something?” she asked, taking in the familiar décor of stained glass windows and marble columns illuminated by lanterns. This place had been a second home to her for much of her childhood, and Celestia had never once refused her entry. “Have you changed the rules?” She looked aghast at this prospect.

        Hiding her smile behind a golden-shod hoof, Celestia managed to keep a wry chuckle suppressed; there were few things in life that would never change, and it looked like Twilight Sparkle's penchant for order and regulation was one of those things. “That's not quite what I meant, my little pony,” replied Celestia, recovering her composure quickly and speaking in the smooth, gentle register that she was most known for. “I simply thought that you were acclimating to your life in Ponyville with your new friends.”

        “Oh!” Twilight said, smothering the urge to smack herself on the forehead for her stupidity. “I was. I mean, I am.” She took a deep breath, wondering just what it was that made her so tongue-tied in front of her mentor. It seemed that her childish desire to impress Celestia hadn't quite abated as she'd matured, plus there was the fact that her presence was just so … overwhelming: that sparkling mane, those intelligent eyes, the relaxed yet alert mien. Starting again, she said, “There were some things from my old room that I wanted to take with me to the library, so I thought that I'd pop back and pick them up. Just a few, uh, mementoes. Trinkets. Nothing really special.”

        “Your Smarty Pants doll?” Celestia asked mischievously.

        Twilight's face turned cherry red. And of course, there was her famously droll sense of humour.

        “Thought so.”

        For a long moment, silence reigned; Twilight considered resuming her search, but something seemed off with her mentor. Of course, the last couple of weeks had been a very busy time for her, but she should be happy about that, right? After all, it wasn't every day that one welcomed home a long-lost relative. “Is something the matter?” she eventually asked with some trepidation.

        “No,” replied Celestia, narrowing her eyes and frowning. “Why would there be?”

        Biting her lip, Twilight wondered if her sister's return was one of those touchy subjects that she ought to leave alone, but – as her books on assertiveness had so assiduously put it – nothing ventured, nothing gained. She was new to this whole friendship thing, she knew, but Twilight now realised that Celestia was, in fact, her oldest, dearest friend and that meant … something, didn't it? Didn't it give her the right to ask? “How are things going with Princess Luna?”

        “It's just Luna. For now, anyway,” said Celestia, a gloomy look crossing her muzzle that Twilight couldn't immediately identify and wasn't at all sure that she liked seeing. It was gone in an instant, however. Maybe its supposed eeriness was just a trick of the lantern light? “Her titles had been revoked in absentia long ago, and whether or not they'll be restored to her is a decision for the Council of Unicorns to make.”

        “I meant … how are things with her? Is she okay?”

        “Physically and mentally, she seems to be okay, at least according to the finest doctors in Canterlot,” Celestia said, stroking her chin thoughtfully as her eyes drifted in the direction of a certain door halfway down the corridor. “If she bears any scars of her time with Nightmare Moon, they are well-hidden.”

        “That's good,” said Twilight. “I'm not so sure how I'd feel if I'd been trapped in one place for a thousand years.”

        “It wasn't a thousand years for her.”

        “Huh?”

        “It's difficult to explain, but the prison in which she was held operates on a slightly different timestream to that of Equestria. To cut a long story short, from Nightmare Moon and Luna's perspectives, it would only have felt like a matter of days that they were gone,” Celestia said, tears forming in her eyes as she replayed those final moments in her memory once more.

        “I'm sorry for bringing this up,” Twilight said, feeling uncomfortable and scraping apprehensively at the floor, unsure whether or not to just leave her mentor to her brooding or to try and make amends for her fumbling approach at being a good friend. She decided on the former. “I should get going now.”

        “Stay,” Celestia said in a quiet, almost depressed, voice. “Please?”

        “What is it that's troubling you, Princess?” Twilight asked, placing a hoof on one of Celestia's forelegs. Maybe she was crossing a line, maybe she wasn't cut out for this friendship malarkey, but she just didn't care at the moment. Somepony that she cared about was hurting, and she needed to know why. Needed to know how to fix them. If she could.

        “Isn't that supposed to be my line?” asked Celestia, shooting Twilight a thin, though genuine, smile. “Still, at least you didn't refer to me as your little pony.”

        “Sorry, I didn't mean to come across as patronising,” Twilight said sheepishly, blushing once more.

        “It's all right, Twilight.” She patted her student's withers affectionately. “As it happens, yes, I am troubled, but not by Luna's return. At least, not per se.”

        “What is it, then?”

        “The circumstances that put her on the moon in the first place are still a source of frustration to me,” said Celestia, her darkly melancholic expression suggesting that frustration was serving as a polite replacement for another word entirely. That grim look on her face was only enhanced by the embers of flickering torchlight. “I've had a thousand years to think about what happened, and barely a day goes by where I don't replay the event in the hopes of divining some other solution.”

        “Was there one?” Twilight asked tenderly, knowing that, even if she found one, there was a fat lot of good that it did now.

        “No.” Celestia lit out a soft hiss between gritted teeth.

        “You did what you had to do. You can't blame yourself for that.”

        Celestia's expression turned quizzical and she glanced at Twilight. “What do you mean?”

        Just for a moment, Twilight hesitated before replying. I guess this is still a sticky subject. She felt a curious lump of fear forming in her stomach. “Banishing Nightmare Moon with the Elements of Harmony. You had no other choice since your primary responsibility was to keep Equestria safe.”

        “Twilight, I didn't banish Luna,” Celestia said flatly. With dawning realisation, she added, “Of course, I'm such an idiot. How could you have known?”

        “Known what?” asked the perplexed unicorn. “All the history books say-”

        “-I know what the history books say. Who do you think it was that influenced their writing?” said Celestia, shaking her head several times as numerous memories flooded unbidden to the forefront of her mind. “Equestria was undergoing a period of upheaval at the time. Not just because of Nightmare Moon, I should add, though she was certainly bad enough. Enemies or potential enemies surrounded the entire country, and it was necessary for my little ponies to believe that they had a strong, capable leader who could take decisive action in a crisis situation. What better example than having my own sister expelled when she fell to the forces of darkness?”

        Twilight absorbed this with her mouth agape. Books were sacred, a way of passing information down from one generation to another, and if they couldn't be trusted … what, then? To know that her own beloved mentor had wilfully distorted facts just to win a propaganda war …

        “Could you please stop looking at me like I just told you I was a Changeling Queen,” Celestia said, but there was no amusement in her voice. “I did what I did because I though it was the right thing to do at the time.”

        “What really happened?” asked Twilight, trying to put herself in her mentor's position. She could see the logic in a fractured nation needing to be united under a strong leader, anyway. “To Luna, I mean?”

        “She banished herself. More accurately, I suppose, Nightmare Moon did. I tried to use the Elements of Harmony to stop her from doing it, or at least to stop her from taking Luna with her, but I failed. The Elements failed, whichever.”

        “But why did Nightmare Moon do it?” Twilight asked, eyes narrowed. “Why would she willingly imprison herself for so long when she could've escaped, fought back? She must've known what was going to happen, that you would have time to prepare for her return?”

        “She did it to punish me.”

        “Punish you?”

        Celestia's gaze turned to the roof and she fought the tears welling up in her ducts. “My bond with Luna was the most precious thing in the world to me. Like all siblings, we fought, of course, but I never thought anything of it. I never realised just how close to the brink she was until it was too late to help pull her back.” She retrained her attention on Twilight. “Nightmare Moon won a great victory that day. By denying me the company of my sister, by forcing me to live through a thousand years without her, she weakened me considerably. Negative emotions sustain her power, in much the same way as a Changeling feeds on love, and doubtless she hoped to use this energy to defeat me upon her return.”

        Nightmare Moon was a parasitic entity; it sought out the angry, the depressed, the jealous – in Luna's case – and promised to give them exactly what they wanted … so long as they bowed to her wishes. Its wishes. Celestia still wasn't certain if it was even identifiable in such corporeal terms. Her sister had grown resentful over the adulation that she'd been given for raising the sun while her moon went continually unnoticed; she'd hoped that they'd be able to sort things out, heal the rift that had grown between them, but Luna had constantly rebuffed her advances until … she'd simply decided to stop making them and trusted that Luna would see her way out of the darkness on her own.

        “So … she was the one who got out the easy way, while you had to take the slow path? I'm sorry,” said Twilight, “I had no idea.”

        “As you can imagine, it's not a subject I'm all that comfortable with talking about. To anypony.”

        “I understand,” Twilight said, eyes half-closed. “Thank you.”

        “For what?”

        “For telling me. I know it must've been difficult to do so, and I appreciate your trust. I appreciate you letting me see this side of you, finally.”

        “You're one of the few ponies I trust implicitly, Twilight Sparkle,” Celestia said. “Maybe I should have told you about this sooner, but though you aren't fully-aware of this yet there is a certain pattern to our lives and things will have to unfold in a certain way.” Off Twilight's confused look, she added, “Never mind. It's not important. Not just now.”

        “You should talk to your sister about this. Put the ghosts of the past to rest or at least make peace with them,” Twilight said, following Celestia's eyes down the corridor.

        As the a particular door halfway down the corridor opened, Celestia said, “I may do just that.” A group of white-clad ponies, some of them muttering over clipboards and charts held in their magical grasp, surrounded a rather dishevelled-looking dark blue alicorn.

        “Sister!” Luna said delightedly upon spying her older sister. Her expression was not slow to turn to annoyance, however, when she felt yet another arcane instrument connecting with a sensitive spot on her body. “How much more of this vexatious poking and prodding must I be forced to endure?” she asked, shooting her coterie of physicians and psychologists a dirty look. “These witch doctors and charlatans of yours can rest easy knowing that I am perfectly fine!”

        Exchanging a look of amusement with Twilight, Celestia said, “Unfortunately, the poking and prodding will have to continue until the Council of Unicorns is satisfied that you … no longer pose any danger to us. Which, I hope, will be nothing more than a mere formality at this stage.”

        Luna opened her mouth, intending to make some kind of impassioned argument about the useless shrubs who occupied the Council of Unicorns, but at a warning look from Celestia she decided otherwise. “Very well, then.” She offered her sister a fleeting smile. “If I am allowed to do so, I look forward to ruling alongside you again. I can only hope that, in my absence, the ponies of this era will come to appreciate a night done properly.”

        “I certainly will,” Twilight said, then immediately clamped her hooves over her mouth. She'd been silent for so long that she'd started to fear that she no longer knew how to speak. “Er, that is to say, one of my hobbies happens to be astronomy.”

        To her great relief, Luna favoured her with a bright smile. “Thank you, young miss. I shall show you such splendours as you have never seen before!” Feeling a tug on one of her forelegs, she let loose an enormous sigh that was analogous to a balloon quickly deflating. “Yes, very well, let's keep this procession of embarrassing aesculapian procedures on the move by all means.” To Celestia: “Shall we have dinner tonight, assuming that there's anything left of me to have dinner with, and … talk things over?”

        “I'd like that,” replied Celestia warmly.

        With that, Luna finally allowed herself to be led away by her retinue to the Council of Unicorns; there, she would no doubt be subjected to further tests, further questions, further scrutiny, but she knew that she would win their trust in the end.

        After a suitably agonising length of time had passed, Twilight finally asked Celestia, “Are you going to be okay?”

        “You know what? I think I just might be,” replied Celestia, smiling radiantly at her student. “Thank you for taking the time to talk to me, Twilight. Driving myself crazy with these pointless thoughts about what happened isn't going to do me, Luna or anypony else a lot of good. I have to make my peace with the past, and the way to do that is-” she sighed happily “-by reconnecting with my sister and putting the spectre of Nightmare Moon behind us once and for all. For the first time in ages, I actually feel good about contemplating the future.”

        “Always happy to help,” said Twilight, trying to contain her excitement; being praised for doing a good job felt wonderful, and never was it more satisfying than when it was Princess Celestia herself doing the praising. There was no feeling in Equestria quite like it. Except, perhaps, finding a pristine First Edition in the library. “Now I need to get back to finding my Smarty Pants doll. I was so sure that I left her in my room. Maybe one of the cleaners accidentally threw her out?”

        Before Twilight could work herself up into too much of a fret about that possibility, Celestia said, a slight flush tinting her alabaster cheeks, “Actually, she's in my room.”

        “What? Why?”

        “Because,” Celestia said, turning away so that Twilight couldn't see the full extent of her embarrassment, “not all of my memories of the past are bad ones. You are very special to me, too, and I wanted to have something of yours to remember you by while you were in Ponyville. When I found the doll in your room, I decided to keep hold of it.”

        Not quite sure how to feel about the fact that Celestia had been hoarding something so precious, so personal, of hers, Twilight said, “You can keep her if you like? She's only going to end up in a box in my room at the Golden Oaks Library, anyway.”

        “No, it's all right,” said Celestia, feeling abashed about the situation. “Just promise me that you'll swing by the castle in between your friendship lessons to visit us?”

        In that moment, Twilight had a revelation about her mentor: losing Luna had given her some deep-seated abandonment issues and it was only natural for those feelings to extend to other ponies that she was close to. She couldn't bear the thought of losing somepony else that she cared about. “Of course I'll stop by,” Twilight said with a sly grin. “You don't think I'm gonna give up my lifetime pass to Canterlot Library, do you?”

        “Of course.” Celestia chuckled, remembering how Twilight's face had lit up like a Hearth's Warming tree when she'd gifted her the pass upon her successful admission to her School for Gifted Unicorns. “How could I forget the library? Your one true love.”

        “I'm sure I could spare a moment for you, too, though,” Twilight quickly added, nuzzling against Celestia's side. Going off to Ponyville, learning more about the magic of friendship, was a big deal – a brand new chapter in her life's story – but it didn't mean that she was going to forget her roots. Or the ponies who'd been her friends before she'd even known what friendship was all about.

        Returning the nuzzle, Celestia was grateful for both the physical warmth of Twilight's body and the greater hear generated by their bonds; with Luna back, she felt as though they could overcome any obstacle so long as they faced it together.