The Sideways star will play Cora’s “maverick, playboy brother” Harold in this year’s Christmas special, alongside Shirley MacLaine as Martha Levinson.

Executive producer Gareth Neame commented: “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 Christmas Day episode.”

Series 4 will air on ITV later this year.

Giamatti is currently filming The Amazing Spider-Man 2, which arrives in cinemas next summer.

What are your hopes for Series 4? Let us know below…

> Order Series 4 on DVD on Amazon.

> Buy the complete Series 1-3 boxset on Amazon.

Watch the Series 3 trailer…