Monsters · 3:05am Aug 8th, 2015
When I started writing the interaction between Nightmare Moon and her Nemesis, I originally planned for Nightmare to reveal her origins. However. . . I changed my mind for a few reasons:
1. If I used my own favored explanation for where Celestia and Luna came from, it would actually be a bit of a spoiler for a couple of other stories -- currently on hiatus but I do plan to get back to them.