Twilight wants to know what happened to Starswirl the Bearded, but nopony who knows will speak. How many wounds is Twilight ready to reopen to get her answer?
In a string of theories, I concurred this one while working late at night. I don't intend to make it extremely detailed, but more-so as a way to explain some things about a couple of the most mysterious ponies ever mentioned.
Thanks to the following for finding errors:
Starlight Nova
EDIT: As I'm sure some of you have read the comics- namely the 'Fiendship Is Magic' series- you know that the story behind Sombra is different. I had written this beforehand and will just leave it up for others to read.