The Crystal Heart Spell is a pony book with an expected launch of April, but people that visit Scholastic bookfairs can pick it up a bit early (usually an elementary school thing). The big thing here is the actual content. While I can't check it here in front of me, the submitter (Sergio) is saying that it is a direct followup to the season finale, though the cover doesn't really hint at that. The expanded synopsis on the back gives a bit of added information:
A royal event has turned Twilight Sparkle's life upside down. To learn how to handle her new status, Twilight goes to Princess Cadance for some guidance. The princess shares her own story about how she came to rule the Crystal Empire and a magic spell that helped her follow her heart. Inspired by Princess Cadance, Twilight Sparkle sets off on a quest for the Crystal Heart Spell!