Luna's banishment happened near the start of the Nightmare war, and Celestia, in her grief notices far too late what horrors her loyal forces had wrought, so with a heavy heart, she seals them all away. A thousand years later an exiled knight from the former lands of Shining Dawn shows up mere days after her beloved sister's purification and return. To her surprise the knight, descended from generations of those Solar zealots swears fealty, not only to her, but her sister as well. Having little use or want for a living reminder of her past mistakes to the night ponies, she sends him to Ponyville to watch over her faithful student, Twilight Sparkle.