ABC’s “Once Upon A Time” just made another huge casting announcement.

After finding the actors who will take on the roles of Elsa, Anna and Kristoff in next season’s “Frozen” crossover, the storybook drama is adding a “Lost” alum to the cast for Season 4. Elizabeth Mitchell, who played Dr. Juliet Burke on “Lost,” has just signed on for a mysterious new role on the hit ABC series. Mitchell’s character, who may or may not be the show’s new villain when it returns, will have ties to the trio from Arendell and her story arc will also have her crossing paths with some of our favorite residents in Storybrooke.