Molest Tear or Morestia identity is the dark side of Celestia. If Nightmare Moon is the dark side of Luna that was born from resentment. Thus Molest Tear is the dark side of Celestia that was born from suppressed of lust. For to be a good leader that love will not distracted her work.
Molest Tear was separated from Celestia by Celestia's lover and became an Unicorn that you just seen in picture.