PARK CITY, UT - JANUARY 21: Actor Paul Giamatti poses for a portrait during the 2011 Sundance Film Festival at The Samsung Galaxy Tab Lift on January 21, 2011 in Park City, Utah.

The Emmy-winning actor will appear in the acclaimed PBS drama's season-four finale.

Paul Giamatti has joined the cast of Downton Abbey and will make his debut on the acclaimed PBS drama in season four's finale, the broadcaster announced Monday.

The actor -- who won an Emmy, a Golden Globe and a SAG award for his portrayal of the second U.S. president in the 2008 HBO mini-series John Adams and often portrays bumbling and self-doubting characters -- will play against type as Cora's "maverick, playboy brother Harold," said PBS.

He'll star alongside Downton cast members, including Shirley MacLaine and Michelle Dockery, as well as new faces Tom Cullen, Joanna David and Gary Carr.

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"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," said Gareth Neame, managing director of Carnival Films, a co-producer of the series.

"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," teased Neame.

Giamatti, whose eclectic film credits include Sideways, The Hangover Part II and HBO's Too Big to Fail, is currently filming a role as villain The Rhino in Amazing Spider-Man 2, slated for release next year.

Downton's fourth season premieres Jan. 5, 2014, on PBS.

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