Twilight has an interesting conversation with Sparkler when she finds her sitting on a park bench all by herself, looking very depressed. To Twilight's dismay, SHE'S the reason Sparkler is so upset.
After a conversation Princess Celestia has with her student, she decides it'd be best to address her issues and bring closure to a secret Twilight has kept for many years.
The past always comes back to haunt the present, there is no escaping the inevitable. For decades, Celestia has kept a secret from her student. A secret she made out of pain, and through pain will be revealed for all to see; for Twilight Sparkle is