Paul Giamatti joins 'Downton' as American playboy By Nuzhat Naoreen, EW.com June 24, 2013 -- Updated 1931 GMT (0331 HKT) Paul Giamatti has been cast as a guest star in the fourth season of "Downton Abbey." Paul Giamatti has been cast in season four of 'Downton Abbey' as a guest star He'll portray Cora's playboy brother Harold Season four of 'Downton' will begin January 5 (EW.com) -- "Downton Abbey" is getting another American visitor. "Sideways'" star Paul Giamatti will appear as Cora's playboy brother, Harold, in the season four finale, a rep for Masterpiece on PBS confirms. 'Downton Abbey' casts first black cast member He'll be joined by returning guest star Shirley MacLaine, who crossed the pond to play Cora's brazen mother, Martha Levinson, in season three. 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's apple cart in this year's finale," executive producer Gareth Neame said in a statement. New 'Downton' characters announced Giamatti is hardly the only new face joining the series - next season will introduce a slew of castmembers, including Dame Kiri Te Kanawa, Tom Cullen, Julian Ovenden, Nigel Harman, Joanna David and Gary Carr. Season four of the series will kick-off on January 5, 2014. See the original story on EW.com.