Prophecy be told about a pony from a lost era that will bring up memories that the Princess would rather forget, but will inadvertently shed light on a conspiracy that would have saved the lives of thousands.

When Twilight and the gang discover a strange magical pony, unlocking his mysterious past may lead to some more unsettling discoveries about Equestria's history, and show that Celestia's past isn't as clean as they thought.

She's also been assigned as his Warden. To put it lightly, her life is going to be flipped on its head, in more ways than one