After an accident involving one of Starswirl's objects, Luna gets turned into a stallion. She'll have to contend with judging nobles, romantic mares, paparazzi, and her obnoxious sister in order to find a way to turn her back.
He's the God Emperor of Mankind, and she's Princess Celestia of Equestria. With these two dating, you can expect almost anything to happen. Hopefully Equestria survives their relationship in one piece...