(End lyrics are from "Lullaby for a Princess" by ponyphonic. I'm unsure if only using an excerpt of a song goes against 's rules and guidelines. If it absolutely does, let me know and I'll edit it or take it down.)

Twilight knew she had broken the rules. Living, working and learning in Canterlot's castle was a privilege, her parents had said. They had told her time and time again that such an opportunity hardly came once in ten lifetimes, and that she was completely indebted to the princess who had given it to her. So she had listened patiently as the castle guard drilled the rules of the castle into her head over and over until she could recite them backwards and forewords: No inviting people inside without asking permission, use proper manners in front of guests, and most importantly, never under any circumstances wander the castle grounds after dark without supervision. And never before had she even dreamed of breaking them.

But still, here she was, standing on the balcony of Princess Celestia's room, a night guardsman at her side giving her a stern glare. The aforementioned royalty, who was sitting and staring into the night-shaded landscape, now turned to face them.

"Good evening, Sentinel. What brings you here?" She asked, growing even more puzzled when she noticed her young student staring at the ground, a look of shame plastered on her face. "Is something wrong?"

"Ma'am." The broad white stallion began, "I was performing my rounds when I found Miss Sparkle sneaking around the halls outside your room."

"I wasn't sneaking!" The lavender filly cried defiantly, though her volume dwindled when Sentinel sent her a hard look, "I-I heard a noise and couldn't sleep…."

The guard rolled his eyes, but Celestia cocked her head in curiosity.

"A noise?" She asked. "What kind of noise?"

"W-well, it kind of sounded like…."

"Sounded like what?"

Twilight shuffled her front hooves. "Well…like singing."

For a moment, no one spoke. Sentinel glanced at Princess Celestia who seemed to be thinking. Twilight awkwardly waited for one of the adults to speak.

Finally, Sentinel cleared his throat. "Well, if you'll excuse us then, Princess, I'll be taking Miss Sparkle back to her quarters - ."

"That won't be necessary, Sentinel. You may return to your rounds."

The stallion was surprised, but nonetheless bowed. "Of course, Your Highness." With that, he left the balcony and exited through the bedroom door without questioning his liege's orders. Twilight gulped anxiously, afraid she had just blown her chances of learning magic with the land's sovereign monarch.

To her surprise, Celestia smiled and motioned for the filly to take a seat beside her. With anxiety rushing through her, Twilight slowly approached and sat next to her teacher. The scene was unnervingly quiet.

Twilight broke the silence. "I'm sorry, Princess."

Celestia laughed softly. "No need, Twilight. In fact I should be the one apologizing for keeping you awake."

Twilight looked up, incredulous. "That was you?"

"Indeed."

"I didn't think you could sing. I-I mean, I've never heard you sing before."

"I'm afraid I'm often much too busy to. This is really the only time I can." Celestia sighed in a tired sort of way, "When everypony is asleep, I mean."

"So then who do you sing to?"

"To myself, to the stars and to Canterlot." Her voice grew soft. "But mostly to the moon."

"The moon?"

Celestia nodded. After a brief silence, she chuckled. "That must sound a little crazy, to sing to the moon."

"Not really." Twilight turned her attention to the familiar constellations that she had memorized since her last astronomy lesson. "In fact, I think the Mare in the Moon likes it."

For the first time in centuries, Celestia's heart skipped a beat.

"What...do you mean?"

"See," Twilight continued. "Everybody's always asleep at night, so when the moon comes out and the Mare in the Moon looks out on us, nobody's there. I think that makes her really sad and lonely. So I think it's nice that you sing and keep her company." She looked up at her mentor and smiled, "I think it makes her feel like someone cares."

Celestia could almost see her own stunned expression in those huge innocent purple eyes. The child's words were like a storybook, recounting scenes from a time far far away. She was so naïve, but somehow understood more than she would ever know.

"Princess?"

The white mare shook herself out of her stupor. "Yes?"

"If it's not too much trouble…." Twilight asked tapping her hooves together nervously. "Can you sing for me?"

"Sing?"

"Yeah…i-it was really pretty.."

Celestia didn't speak for a moment. Then, a gentle smile that reminded Twilight of her own mother spread across her teacher's face.

"Of course."

So that night the princess of the sun sang before an audience of the moon, stars and one small filly who eventually drifted off to sleep, leaning into her mentor. Though hardly anyone would take notice, the faint haunting melody that came from the castle in the dead of night sounded a little happier that night and every night after.

And sometimes, never once stopping to ponder just whose ears the lyrics were meant to reach, Twilight would look up at the starry sky and sing the curious chorus she remembered before sleep overtook her that night.

Lullay moon princess, goodnight sister mine

Rest now in moonlight's embrace

Bear up my lullaby, winds of the earth

Through cloud and through sky and through space

Carry the peace and the coolness of night

And carry my sorrow in kind

Luna, you're loved so much more than you know

May troubles be far from your mind

And forgive me for being so blind