When King Sombra returned for the second time, Princess Cadence wound up discovering the true origins of her birth, throwing her whole world out of whack and causing her to question her own identity. In order to solve this dilemma, she journeys to Canterlot to visit the ponies she's known her whole life as "Mom and Dad" in order to hear the truth from their mouths.

*Part of my head-canon universe

Takes place between When Darkness Falls and The Return of the King

I would suggest reading When Darkness Falls first as this contains spoilers

An extra-special thanks to Viper Pit for the concept!