New 'Once Upon A Time' Season 4 Teaser Reveals Return of Major Character (VIDEO)

Once Upon A Time returns for Season 4 this Sunday at 8:00 PM on ABC, and it's the most hyped season since the show's first, due to the introduction of Disney's Frozen to the show's narrative. But this latest teaser has absolutely nothing to do with Frozen. In fact, it has to do with the show's own history, as this video clip reveals the return of a character we haven't seen in a long time.

In this clip, Regina (Lana Parrilla) returns to Storybrooke's sanitarium to get the one ally she feels she can depend on when her happiness is threatened. So what does Regina have in store for her mystery ally? And for Emma (Jennifer Morrison), who has inadvertently caused the end of her relationship to Robin Hood? Hell, what does Regina have in store for Storybrooke, in general? Check out the full video below: