6000 years

Celestia sighed in relief, her pupil was now in the final stage of taking over leadership of Equestria in her place.  The young mare was taller now, almost as tall as Luna, her mane was longer, and having a less tendency to get frazzled. She had matured in so many ways Celestia couldn't count them all. She was growing up.

There was a fact about alicorns, only Celestia and Luna knew this sacred secret. Alicorns weren't immortal. Nobody knew.. But the era of Celestias rule was coming to an end, millennia after millennia had taken a toll on the alicorn, not a physical effect, but an effect on the soul.

The Princess flashed back to the hallway of moments twilight had spent with her friends, she was truly ready for the responsibility of Princess. Making her precious student an alicorn began the process of Celestia dying, the beginning process of her soul slowly dissolving away, half of her soul moving into twilight, the rest moving into her celestial body, the sun, of course. Where she could watch over her country for millennia after millennia to come.

The Princess was Dying, and nothing could stop the process of death, even the spirit of death itself.

A single tear fell from Celestia's eyes, onto the old wooden desk she had chosen out herself all those years ago.

Wiping the growing tears in her eyes away, the alicorn stood up, turning around, only to meet eyes with her sister, a thousand years younger than her, the nightmare had paused her age and growth rate all together. " Tia? Are you alright? " the pain struck Celestia in the heart, the fact that she would be going before her sister, another thousand years without the dark blue mare she had come to know. " Lu Lu... We.. We need to talk. " Luna's expression darkened, you could see her bracing for the pain of the certain talk they had put past so long.

Together they walked to the balcony, sitting down beside each other, overlooking the great country they had ruled for last 9 years. " Sister... You are aware of an alicorn's life span.."

The princess of the night seemed to shrink, a mix of emotions flowed through her mind all at once, all she could do was sit there and murmur, " 6000 years... Earlier if.." Referring to Twilight's case. Celestia responded with pain in her voice, " Lu Lu.. I know your thinking about the thousand years we spent apart...how much we time we lost-" Luna suddenly broke.. Crying into the Sun Princesses' shoulder. " Oh Luna.. Please don't cry..I will always be there-" " But you won't Tia...  I was the one that agreed with your decision to make Twilight your successor.. I'm the reason why you won't be here..." The moon princess began to sob, explaining her fears and blaming herself at heart, only to be silenced by a comforting hoof to her lips and a quiet shush. Celestia got off the tall bench and sat on the ground to where she was at eye level with her sister, putting aside all their worries with a priceless hug.

No words could explain the pain that they shared, it was something they shared down to the bone.

They sat there, just hugging, willing it to continue. Like all good things, it had to end, surprisingly.. Luna broke the silence, her voice raised more than a murmur. " I know your d..dying Tia..."  Celestia closed her eyes,  eyes flashing open. " But you know what? " Her voice barley a whisper, but with confidence. "What?"

" I will always be with you Luna, always, right here " Placing a hoof onto the smaller ponies heart. Both princesses smiled lightly, embracing another hug, tears falling freely, not of sadness, but of joy.

Both unaware of  the lavender alicorn, sitting on the underneath balcony, weeping , now aware of her fate.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Luna had trotted off to Night Court as soon as she finished her dinner, leaving Celestia alone at the table. Surprisingly Twilight had not come to dinner, but that wasn't uncommon. That mare could read books day after day surviving on nothing but Twinkies and water.

Sighing, Celestia got up, nodded thanks to the cook, and slowly walked her way to the newest Princess's chambers. Once again she was reminded of how large the castle was and how empty it had always been. The coronation of Twilight 4 years ago gave new life to the castle for a week, giving Celestia flashbacks to the first days of the Two sisters rule. The pristine marble had lasted so many years, it was difficult to tell if they had actually put it in 1000 years ago, and not just replaced it. Before the alicorn could get to deep in a walk down memory lane, she had reached her destination.

Opening the ornately carved mahogany door,  it revealed the candle-lit room, shelf after shelf of books lined the walls, the ceiling far above my head, revealing a very large portion of Luna's constellations. If I was correct she was planning on adding a glimpse of the Milky way tonight. Twilight should be here, the astronomy lover wouldn't have missed this. But in place of the lavender alicorn was a single scroll.

Dear Princess Celestia,

By the time you read this its probably after dinner,  your wondering why I'm not at my quarters admiring the stars. I needed to take a walk... I overheard Luna and yourself this afternoon.

The world started spinning in my head... shock.

I just wanted to ask you something...

Why?

Why didn't you tell me?

Do you really trust me with the leadership of Equestria?

Your faithful student/colleague,

Princess Twilight Sparkle

P.S.

If you need to speak to me in private, I'm currently at the small forest outside the castle, skipping stones. Philomena is keeping me company.