Just before leaving for her honeymoon, the newly-married Princess Cadance finds her old diary in her clothing dresser, filled with memories long forgotten, where she then recounts on those happy days as Twilight Sparkle's foalsitter. (Featured on EqD!)

Image credit goes to Bufko

When Twilight receives a letter from Princess Celestia asking her to come to the castle for something very important, Twilight is puzzled. What Princess Celestia and Luna have to tell her will change the Unicorn's life forever.