The future is now, but the past still burns
Why was Celestia so surprised when a baby Alicorn was born? It seems like basic genetics, right? Unicorn horns and Pegasus wings are dominant traits as shown by the Cakes; and with an Alicorn mother, wouldn't they be dominant here too? So what reason did she have to be surprised? Unless this has happened before, with a different result.
1000 years is a long time to be alone. Over the generations, one is bound to get attached to a pony or two. Usually just as friends, or even close pupils. Sometimes though, well, everyone has urges.
That is why Celestia is so confused, so hurt at the moment. Why? Why couldn't it have been this easy for her?
The baby is beautiful. Bright eyes, powerful magic, and strong wings. The perfect powerhouse of a baby. Most likely also immortal. So why couldn't hers have been?
Maybe it was the love that produced an Alicorn. After all, the few times she had ever shared her bed, it hadn't ever held the same level of love. She had been fond of them of course - but they were so much younger, and would be gone so quickly. If she fell too far in love it would just hurt even more later.
(Maybe that's why her baby boy didn't live long either, maybe if she loved more he would have.)
He was so cute, so strong. A young Unicorn with an overwhelming urge for knowledge. Equestria was still young back then, her sister not long gone. He helped fill the void so well, and she was so happy to have him. Until he hit adulthood and didn't stop aging, that is. She tried to stay close-she truly did- but it was so hard when she knew; knew he would soon be gone, just like all the others.
(They grew apart.)
He never had kids of his own, never fell in love. He spent his life cementing his place in the history books. She always felt remorse at that, wondering if her lack of sharing love is why he never got to have any of his. It was a parents job to love their children, after all.
(She wasn't a very good parent.)
And as most living creatures do, he aged, he died. She hadn't ever truly publicly announced their full relation. (It wouldn't do for the Princess to get a reputation, now would it? Illegitimacy was still frowned upon in those days.) As a result, when she attended his funeral she attended it as a teacher-not a mother.
She mourned alone later. She mourned her lost son, her only heir, the future they could have had-if only he had been immortal. Maybe that was the problem though, wasn't it? She was so sad over what he could have been, that she hadn't enjoyed who he was while he was there. The pain would never go, never truly fade. She had lost what no one should have to, and she lost it long before he died. She had lost her child. She never wanted to go through that pain again.
(She invented the contraception spell after that.)
So here she was -over 900 years later- looking at a cross-bred Alicorn baby. (A Unicorn father and an Alicorn mother, just like hers.) She smiled and congratulated them. She stayed by their side and protected what she could. She left them with pride in her eyes.
And when she went home? With her sister here to help, and the pain resurfaced? For the first time in centuries, she told her story and wept.
Luna's sleeping schedule was already off enough from the events at the Crystal Empire. Upon arriving home, she realized it wasn't getting better anytime soon. It was still day, if she got some sleep now she would be up in time for her nightly duties. As soon as her sister got in the castle though, that was obviously not an option.
She had never seen her sister cry. Her strong, proud, unbreakable sister. Even her betrayal hadn't been enough to bring tears to her eyes. (Well, at least not in front of her anyway.) So when Celestia broke down with a tale so old, yet so raw at the moment, all she could think to do was hold her sister and listen.
It took hours. Between the sobs and the stutters it took four hours to get the basic of the story. She talked about her baby being born, how she did it herself and hid him away. She talked about him learning to talk, to levitate things, to walk (in that order). She talked about when she enrolled him in her recently created magic school so that he could grow stronger among peers. She talked with such pride, so much joy and sorry intermixed.
Then she talked about him growing up - and not stopping. She talked about him growing smarter, stronger, and them growing apart. And after they grew apart, how it felt like she had barely blinked before he was gone.
(Ponies do die too fast, even with her thousand years of banishment Luna still remembers the pain from that.)
By the time she was done it was time to raise the moon. For the first time Luna had to tuck her into bed. That completed, she knew she had a new duty to do tonight.
While keeping an eye on ponies dreams kept her busy, that didn't mean she didn't have any time to herself. During that time, she scoured the library for every mention of the stallion of which Celestia had spoke. She found a decent amount. He was a famous Wizard by all means, though no Starswirl. He had managed to make quite a few head ways in multiple different areas of magic. She wondered if her sister knew that among those areas were time spells and aging magic. He was the first Wizard to successfully extend his life with magic, even at the cost of most of said magic. He lived a good 70 years longer than he naturally would have. That was still too short for an immortal though. Still, it sounds like he was trying to stay around for her sister, right until the very end. He was one child though who had no chance of outliving his mother.
By the end of the night she was thoroughly enlightened, as well as completely exhausted. When she went to wake her sister, she looked as perfect as ever. The shields were up; the immovable princess was back. Luna wondered how much practice it took to hide that much pain for so long. After her incident with the Tantabus though, maybe it was best she never try. Maybe it was best she stop Celestia from trying too. Luna was here too now, they can handle their pain together.
After she gets a good days sleep that is.
