I've heard rumors that Johnny Depp played The Joker in a scene or two in The Dark Knight. Is this true?

I've heard conflicting stories. I've heard Christopher Nolan has enough footage to include Heath Ledger in the next installment of Batman, but then my fiance heard that Depp filled in as the Joker for a scene or two after Ledger died. I've read Depp was tapped to replace Ledger in The Imaginarium of Doctor Parnus, so I'm wondering if someone got confused. Help?