Princess Celestia is a love interest of alternated King Sombra.
She's the sister of Princess Luna who is also known as "Nightmare Moon", she was the former enemy of Discord when her and Luna meet him the first time, she was not loved him at all because she want to protect her world from all evil, so she and Luna transform Discord to stone statue when he was amused by their face.
again when discord was released from his statue form by accident, she see her enemy was freed and scared all the ponys from Equestria, so when she tells Twilight and her friends to punish Discord, they transform him into stone statue but with fear on his face. But later she decides to give him a second chance, and put away the stone statue spell on him only if he redeemed himself and finally became friend with him.
But when Discord betrayed the ponies and worked with Tirek, she knew he will return to his evil way again, so her and the other princesses give their powers to Twilight, Tirek imprisoned her, Princess Luna and Princess Cadance to hell jail (Tartarus). When she was finally free, she has her power back, and at the party Discord gave her flowers and made friends with her.
She was also the love interest of the altenated King Sombra, she visit threw the mirror, she fall in love with him when she visit his world with her teacher, but when he find out that she go threw the mirror alone, her teacher get angry and destroyed the mirror before she could say goodbye to the alternated Sombra, but she repair the mirror to continue to see him, but later when she return with the mane 6, she present him to them, but also confronted her evil self. later the alternate Sombra decide to sacrifice himself knowing that the Sombra in Celestia world is a villain, so he decide to be the villain in his world to Celestia and Luna and their friends, so all alternate version of Ponyville became good, but Celestia after Celestia finally return to her world after said goodbye to the ponys from the alternated world, she destroy the mirror herself, and finally said farewell to the alternated Sombra who does the same, knowing that they will not see each other again.
- John de Lancie (the voice of Discord) said...www.youtube.com/watch?v=xIRZpN…