500 years

     Celestia pranced nervously, staring at the moon and Nightmare Moon's face. She closed her eyes and tried to steady her breath, but failed. Hearing hoof steps, she turned, and saw three ponies.

     "Are you sure you want to do this?", she asked.

      "Definitely."

     "You don't have to do this."

     "We know."

     With that, Celestia closed her eyes, and her horn began to glow.