Keeping one eye firmly on the U.S market, where the show is arguably more of a hit than in the U.K (where it is still appreciated, but not with as much fandom), Downton Abbey's producers have made a shrewd move by getting Sideways star Paul Giamatti on board to play the “maverick” brother of Cora, Countess of Grantham.

Gareth Neame, managing director of Carnival Films which makes the programme, 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's apple cart in this year's Christmas Day episode.”

The death of Dan Stevens's Matthew Crawley, who was heir to the Grantham estate, shocked the viewing public. He died in a car accident after visiting his wife and their firstborn in hospital. Sorry, spoilers. But you’re not reading this unless you’ve seen the lot, are you? Downton has been an unprecedented success; it is the highest-rating drama in US broadcaster PBS's 40-year history and has won multiple Emmy and Golden Globe awards.

In addition to Giamatti, Dame Kiri Te Kanawa, Nigel Harman, Tom Cullen, Julian Ovenden, Joanna David and Gary Car will all be joining the growing cast for next year, but fans will have to wait until the feature-length final episode of the fourth series at Christmas for Giamatti's debut.

See more pictures of Giamatti as Rhino in The Amazing Spiderman 2

Paul GiamattiPaul Giamatti won't be doing this in Downton

Paul Giamatti
And he won't be wearing this