The day was an important one. There was no holiday or celebration, but the excitement was present. Queen Harmony was expected to finally give birth to her foal. Many had crowded the Day Court in hopes of seeing the young filly or colt revealed. Within the hour, King Horizon stepped between the curtains, and revealed the young alicorn filly (whom they had named Celestia) to Equestia.
However, not even the king had heard his wife's illness returning. Her pained screams were heard only by the midwife, who quickly rushed to her side. A second alicorn filly was born, who remained nameless. When the king was informed, a look of shock and fear spread actress his face. Only one Alicorn could control the sun and moon, not two. "Luna," as they named her, grew up ignorant that she was in fact Celestia's twin, not just her younger sister. While Celestia was allowed free roam wherever she pleased, Luna was instead confined to the castle, to keep her as a dark secret.
As the years went on, and the king and queen's passing, Celestia (who was fully aware of Luna being her twin) grew paranoid that Luna may try to usurp her. Her anger was noticed by Luna, who had been locked in the castle for her entire life. Celestia had attacked Luna, and used one of the most powerful objects in Equestria: the Elements of Harmony. Luna was wrongfully banished to the Moon, creating the pattern of craters commonly known as Mare in the Moon, and Celestia claimed her spot as the "rightful" Princess of Equestria, hiding all evidence of her sister from the common ponies.
Twilight read the small book with awe, having discovering it between several other books. Strangely, even after she and Spike had reorganized the shelves thrice the previous week, neither had seen The Mare on the Face of the Moon on any of them. It was her first thought that somepony left it there by accident, but the only pony to come to the library the previous day was Moon Lily, who had said it wasn't her book. Twilight was truly baffled by its appearance.
"Spike!" She called for her reptilian assistant, who came running down the stairs. "I need you to take a letter for Princess Celestia, it's important!"
It had been seven minutes since Spike sent her letter to the princess. She had asked several questions about the book, namely about this "Luna" character. She wondered if what the book had told was true, and that Celestia really had banished her own flesh-and-blood sister to the moon. Nightmare Moon also fit perfectly into all of her theories, as she really had been banished to the moon. Twice. Was it possible that she was really Luna? Twilight pondered these thoughts for several more moments, until a breath of fire came from Spike, and formed into a letter.
"Yes! She replied!" Twilight exclaimed, hoping that the princess would lay any of her questions to rest. She unfurled the smaller-than-expected scroll, and cleared her throat.
"My faithful student," She read aloud, "this "The Mare on the Face of the Moon" book certainly sounds interesting, by what you tell of it. But I can assure you, I have never had a sister named Luna, or any sister for that matter. She's entirely a fictional character, Twilight. As for her becoming the Mare in the Moon, perhaps the author mixed up his or her own character with Nightmare Moon's legends? I apologize if this is not the answer you wished for, but it is the truth. Your mentor, Princess Celestia."
Twilight put down the letter in a mixture of confusion and relief. On one hoof, only Princess Celestia would actually know what happened one thousand years ago. Not even the history books went back that far. On the other, however, it made too much sense to be fictional. Could the princess possibly be hiding something from her? That was a definite possibility as well, knowinghow she reacted to Nightmare Moon's initial return.
Her train of thought was broken by several knocks, followed by the sound of the library door opening. Moon Lily followed, carrying a small stack of astronomy books with her.
"Hello, Twilight. I'm just here to bring back the books I checked out." She said, with a small smile.
"Moon Lily, you read all of those books already? Didn't you just check them out yesterday?" Twilight asked, glancing at the thick textbooks. "And they're not small books, either."
"What can I say, I can get sucked into these things."
"You and me both. Let me put these back for you, and you can be on your way."
As Twilight levitated the books back into their rightful spots, Moon Lily spotted the open letter Twilight had left on the center table, picking out "Luna" written several times throughout it. When Twilight wasn't looking, she grabbed the scroll between her teach, and quietly tucked it into her wings, hiding it from view. As she turned towards the door, she barely took a step before Twilight's voice stopped her.
"What do you think you're doing?" Twilight asked, a hint of annoyance in her voice.
"I'm sorry, I just-" Lily stuttered.
"You need to sign your name to show you returned the books."
Stopping in her tracks, Lily let out a small, almost silent sigh of relief, and signed the book quickly. She walked out of the library, and took to the skies once she was outside. Twilight ignored her strange behavior, and went back to deciphering who "Luna" could have been. However, once she turned back to the book, she noticed something was missing. The letter from Princes Celestia was gone.
"Moon Lily!" Twilight half-yelled, figuring out that the mare had stolen her letter.
Moon Lily flew through the air, having grabbed the letter out of her wing. Twilight had found the book she had planted, and was evidently curious about Luna, judging from the princess' mention of her. Just as she had planned. She glided over Ponyville, watching the midday bustle of ponies eating, chatting with friends, and going about their day-to-day business. She flew back to her own home, and landed just outside. It was a modest home, being smaller than most others in Ponyville. She threw open the door, and quickly shut it behind her. The interior was decorated by several crescent moon and star shapes, which resembled the night sky against the blue walls. Moon Lily set the letter down on a table.
Moon Lily read the contents of Celestia's scroll, sighing each time she denied knowing of anypony named Luna.
"Typical Celestia, hiding her past from even her closest friends."
Sad memories came flooding back to Moon Lily, who quickly collected herself, knowing that she would need to return the letter before Twilight came hunting her down.
"Twilight will find out the truth about Celestia soon enough." She said to nopony in particular. "I just need to prove myself to her."
She went to dig out a small wooden box from a cupboard, and set it down next to the letter. She opened it up, and once she laid her eyes on the contents, she smiled, and went to work on her mission. Soon enough, Twilight would know the truth.
Later that evening, when the sun had already set, Moon Lily was on her way to Twilight's library. There was nopony in the streets, save the occasional guard on patrol. She made sure to stay in the shadows when a guard passed her. When she was right outside, she flew up, compensating for the extra weight she was carrying on her hooves. She saw that the window was left unlocked (probably because of Rainbow Dash's antics), and quietly opened it. She didn't want to startle Twilight or Spike, she just wanted to return the letter she stole, with one minor adjustment. Once the window was open, she slipped into the library, and slowly lowered herself to the ground. Her hooves met the wood with a metallic clank, but it didn't appear to startle anypony. Moon Lily quietly walked over to the center table, and reached for the letter. She placed it down, and made sure nothing else was out of place.
"That was easier than I thought." She whispered to herself. "Thank goodness I didn't wake up-"
She was cut off by the lights turning on, and an angry-looking Twilight stomping down the stairs. The alicorn was fuming by the time she reached the floor, and Moon Lily just stood still, knowing that Twilight was already angry enough. Twilight plucked the scroll from the table, and began examining it.
"I knew you stole my letter!" She yelled, noticing a new seal on the letter, bearing a crescent moon. "What does that seal mean?"
"I know what you're after." Lily said, calmly.
"What are you talking about? And what's with the tiara?"
"You want to meet Luna, don't you?"
Twilight became confused by this. "Wait, how do you know about her? Princess Celestia said she wasn't real!"
"Princess Celestia is lying. Who do you think put that book there for you to discover? To make you question Celestia's past?"
Before Twilight could argue with her, Moon Lily raised her wings, and the regalia she wore began to glow. A blue glow began to fill the room, as tendrils of magic swirled around the mare. Twilight quickly figured out that it was a shapeshifting spell, but unlike a changeling's, it appeared much more graceful and powerful. At once, she began to see Moon Lily change. Her head sprouted a horn, and her legs and wings elongated. Her normal dark blue mane shifted to a lighter shade, and the spell began to dissipate. Where Moon Lily once stood, was an alicorn, bearing the regalia and cutie mark of the moon. She could only mutter one word in response.
"Luna?"
