The following is from a Discovery press release. Warning for minor spoilers:
The popular animated series, “My Little Pony Friendship is Magic” from Hasbro Studios, will return for a fourth season on Saturday, November 23, with two all-new, back-to-back episodes starting at 10 a.m. ET/ 7 a.m. PT, on the Hub Network, a destination for kids and their families. Prior to the season premiere, there will be a special airing of the Hasbro Studios’ feature film “My Little Pony Equestria Girls” at 8:30 a.m. ET/ 5:30 a.m. PT.
The fourth season begins with a revealing two-part premiere in which the newly crowned Princess Twilight must balance her new royal duties and her friendship with the other ponies. Amid preparations for the Summer Sun Celebration in Canterlot, Princesses Celestia and Luna go missing and the Everfree Forest is taking over Equestria. These unexpected turn of events sends Princess Twilight and her pony friends on a quest to discover a mysterious foe who threatens to destroy everything. It is all up to Princess Twilight and her friends to help save Equestria from being destroyed. As part of the journey, Princess Twilight is given the chance to discover the secret behind the Elements of Harmony.