Nightmare Moon is now the Mare in the Moon. She left feeling bitter, angry, and hurt.
Celestia is now the only reigning monarch left in Equestria. She's left feeling bitter, angry, and hurt.
Arguments between siblings are.. normal. They're bound to happen. And they're bound to make up sometime.
Right?
Perhaps some letters can... help clear things up. Perhaps.

Big special thanks to Ninjadeadbeard, for editing, prereading, and friendship.
*I do not own the coverart