Centuries ago Star Swirl the Bearded foresaw a pony who, together with her friends, would bring peace and friendship to all of Equestria. This is not that future. The optimal future he and Celestia sought to bring about is no more.

Disillusioned with the pursuit of magic after her failed attempt at enrolling in Celestia's School for Gifted Unicorns Twilight returned home filled with self-doubt. Years have passed and the cynical unicorn wakes to find that the world she knew is no more. Now she must survive the tyranny of a future that never should have been.

A new era has come to Equestria, all hail the Undying Queen!

Mature version here http://www.fimfiction.net/story/303862/the-final-desolation-graphic-version