Paul Giamatti is joining 'Downton Abbey'.
The 'Sideways' actor is to play the part of Harold Levinson - described as a Playboy and maverick - who is brother to Elizabeth McGovern's character, Cora Crawley.
Harold is also uncle to Mary Crawley (Michelle Dockery) and Edith Crawley (Laura Carmichael) in the ITV drama.
However, Paul will not appear until the series four finale, when he will be accompanied by Martha Levinson (Shirley MacLaine), his and Cora's mother.
Executive producer Gareth Neame said: "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.
"We can't wait to see him work alongside Shirley MacLaine, who are both sure to upset the Grantham [family's] apple cart in this year's Christmas Day episode."
Other new characters in the fourth series include Dame Harriet Walters, who plays an old friend of Dowager Violet Crawley, Nigel Harman, who will play a visiting valet named Green, and Tom Cullen, who will be a new love interest for Mary Crawley.
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