Celestia loves Twilight Sparkle. That is a fact, an indisputable constant of the universe. What that love means, however, is much less certain. The love of a teacher, the love of a friend, or the love that Celestia dares not name.
The years have passed well for Princess Twilight and Princess Cadence: the Crystal Empire is prosperous, their ponies are happy, and their love is strong. All is well, until Twilight makes a discovery that will upend their lives forever.