Knights of the Old Kingdom

After the death of a great grandfather she wasn't aware she had, Twilight Sparkle inherits an ancient manuscript documenting the adventures of an exiled unicorn war criminal in the aftermath of Nightmare Moon's rebelion.

But things are never as simple as they first appear, and Twilight soon realizes that there is far more to the story of the mysterious pony known only as the Exile than there first appeared. Twilight Sparkle soon finds herself drawn into a thousand-year-old mystery. Who is the Exile? Why did Twilight's great grandfather have her journal? And why is it that none of this is mentioned in any of Twilight's books on obscure unicorn history?

Loosely based on Star Wars: Knights of the Old Republic 2.