Oscar-nominated actor Paul Giamatti will be joining the cast of Downton Abbey for the Christmas Day special.
The American star, who was nominated for the best supporting actor Oscar for his role in boxing drama Cinderella Man, will play Lady Grantham's brother.
Not a lot has been given away about Giamatti's role in the ITV drama, but producers have let slip the Christmas Day episode will revolve around Lady Rose MacClare's (Lily James) entry into London's high society.
Shirley MacLaine returns as Lady Grantham's mother Martha and James Fox joins the cast as aristocrat Lord Aysgarth.
The two-hour episode of the award-winning ITV series, which will be shown at 8.30pm on Christmas Day, picks up the story six months on from the end of series four.