It was perfect, Princess Celestia was dating her immortal student Twilight, and no mortal pony would ever have her. Tempest, finally free of her guilt, arrives at Ponyville to learn more about friendship from Twilight and her friends. Tempest fell in love with Twilight, and Twilight realizes that she's been missing out on the feeling of true love.

Princess Celestia isn't okay with this turn of events, not in the slightest.
Cover art done by snobbleweb!