Celestia was married in her past life, being of marriageable age and healthy, she was married during her 16th year and by 17 she had borne her mate a healthy son. She does not remember her husband's name, what he looked like, or even if she loved him, now that 2,500 years have passed since she last saw him. Her foal is easier to remember, as she loved him dearly. He was called Horizon Line. 

When Celestia was about 18, the sun died. The heat death of the sun plunged the world into what seemed like an endless darkness. The ponies of her herd, a high ranking one in what is now Canterlot, speculated that a sacrifice would be needed to bring the sun back. At first, the destitute and unwanted were sent to die, but seemingly that was not enough. Over a few short months, almost half of her herd was dead. Being of high status, with a husband and small foal, Celestia assumed that no harm would come to her. She understood that the sacrifices were necessary to bring the sun back, and food was quickly running out, but she dared to hope that her name would not be called on the days when the herd was summoned to choose the soon-to-die. 

By the time she was 19, most of her herd was gone. At last, the horrid day came when she was chosen to die. She tried to be brave, and accepted her fate without protest. Before she left her home for good, she kissed her son and husband, and told them to remember her. She was given a large drink of strong wine, a precious resource hoarded for the occasion. The drink made her placid and yielding, and death came quickly after. She felt sharp and foreign pain, and fell into a white and blue heap, and her essence poured from her thick and dark like wine. 

What happened from here is hazy, a distant memory, a dream. She burst forth, shining like precious gold poured from an opal goblet, flying into this world on swan's wings. Bright and shimmering, she spilled into life with a flourish like powdered sunlight, a glow almost forgotten in these dark times. Following an instinct she could not describe, she lit her horn, and sculpted a new sun into life. A golden disk of light and heat bloomed in the sky like an opening lily, blinding the world with its intensity. 

This newly born mare, fully formed with features of all three pony herds, cantered into this world on a wave of scorching sunlight. She was a Goddess among the people, having formed a sun with of her own magic, willing light and warmth into the dark world. The earth itself, with its boundless magical energy, chose this mare to the guardian of its most precious inhabitants. She bore on her flank a symbol of her divinity, a shimmering sun that poured liquid gold down her legs. She was the first to get a cutie mark, a symbol of a magically ordained purpose in this new life. 

The ponies rejoiced, a month long festival was held, and this mare was installed as Queen of them all, with a great castle to be built over top the scorched lands where she sprung forth from a white hot fire. It was only then that she asked of the herd from which she hailed from, and was told in sullen and hushed tones that all of those ponies were dead, with her own birth burning them all alive, in a great final sacrifice. The Queen's grief was immeasurable. 

They asked what her name was, and she told them that she was Celestia, the Solar Flare.