's Sebastian Stan
will finally make his long-awaited debut as Alice in Wonderland
's Mad Hatter on this Sunday's episode of Once Upon a Time.
And we've got an exclusive sneak peek! First Look: Sebastian Stan goes Mad on Once Upon a Time
While we'll learn how the Mad Hatter became, well, mad in Wonderland, his real-world counterpart, Jefferson, is just as eccentric. Surprisingly...Other Links From TVGuide.com