AceShowbiz -

Paul Giamatti is cast for "Downton Abbey" season 4, PBS has confirmed. The Barney Panofsky of "Barney's Version" will play Harold, the maverick playboy brother of Cora, who comes to Downton with his "free-spirit" ways and both he and Martha "upset the Grantham's apple cart."

Giamatti will first appear in the fourth season finale, which PBS describes as a "dramatic climax." The Emmy and Golden Globe-winning actor joins returning guest star Shirley MacLaine, who plays another American character, Cora's brazen mother named Martha Levinson.

"We're excited that Paul Giamatti will be joining us on Downton to play Cora's brother Harold, the rather free-spirited uncle to Mary and Edith," executive producer Gareth Neame says in a statement. "We can't wait to see him work alongside Shirley MacLaine, who are both sure to upset the Grantham's apple cart in this year's finale."

Giamatti isn't the only actor to make his debut in the forthcoming season of the Julian Fellowes-created series. Gary Carr, Kiri Te Kanawa, Julian Ovenden, Nigel Harman, Joanna David, Harriet Walter and Tom Cullen have been previously added to the cast to play new characters.

"Downton Abbey" season 4 will premiere on January 5, 2014 and air through February 23, 2014 in the U.S. on PBS.

Giamatti was last seen on the small screen as Ben Bernanke in TV movie "Too Big to Fail". The role earned him a Screen Actors Guild Award and a nomination each at Primetime Emmy Awards and Golden Globe Awards. He is currently filming "The Amazing Spider-Man 2" in which he portrays Aleksei Sytsevich a.k.a. The Rhino.