Twilight Sparkle is the Nightmare Moon student. One day, Nightmare Moon invites her to a moonlight gathering on the balcony of the castle.

Twilight vector by Dipi11:https://www.deviantart.com/dipi11/art/Twilight-with-a-saddlebag-289786852
Background vector by Drakizora:https://www.deviantart.com/drakizora/art/Nightmare-Moon-s-Throne-688907199
Nightmare Moon vector by Drakizora:https://www.deviantart.com/drakizora/art/More-Nightmare-Moon-606494753