Remember that offer Twilight made all the way back in "The Beginning of the End"? About Starlight becoming the new headmare of the School of Friendship after Twilight inherits the thrones of Equestria? The offer was genuine...and Starlight accepted it. Now Starlight must prepare herself...Twilight will inherit Celestia and Luna's duties as ruler of Equestria, and Starlight will inherit Twilight's duties as headmare of the School of Friendship.
I loved this episode! The interaction between Starlight and Trixie was great, and it was nice seeing Big Mac again!
Dear Princess Celestia, Today I learned that it's not who you are, it's who you know. Yours Faithfully, Dragonbait