TV Article Paul Giamatti joins Downton Abbey cast By Nuzhat Naoreen Published on June 24, 2013 02:48PM EDT Photo: Brian Killian/WireImage 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. 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," Exec producer Gareth Neame said in a statement. 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 on MASTERPIECE on PBS. Giamatti as a playboy? Are you excited about this new casting announcement?