The Sideways star Paul Giamatti is joining the cast of Downton Abbey alongside his fellow US actor Shirley MacLaine.
But Downton fans will have to wait until the feature-length final episode of the fourth series at Christmas for Giamatti's entrance, playing Harold, the "maverick, playboy brother" of Elizabeth McGovern's Cora, Countess of Grantham.
MacLaine, who had a guest starring role in last year's third outing of the hit ITV drama as Cora's straight-talking American mother, will also be back for the Christmas special.
The casting of big-name US talent is a canny move by Downton Abbey's producers with one eye on the American market, where the show is arguably an even bigger hit than in the UK.
It is the highest-rating drama in US broadcaster PBS's 40-year history and has won multiple Emmy and Golden Globe awards.
Other new cast members for this autumn's new series include Dame Kiri Te Kanawa, the former EastEnders actor Nigel Harman, Tom Cullen, Julian Ovenden, Joanna David and Gary Carr.
The new series will rejoin Hugh Bonneville's Lord Grantham and his aristocratic family in the 1920s, with Carr playing a jazz singer.
Fans were left stunned at the end of last Christmas's final episode by the death of Dan Stevens's Matthew Crawley, heir to the Grantham estate, in a car accident after visiting his wife and their firstborn in hospital.
Downton Abbey's creator Julian Fellowes recently admitted to the Hollywood Reporter that writing Stevens out had been "testing" but unavoidable with the actor leaving the show to pursue other projects.
Stevens apologised in a Radio Times interview for ruining fans' Christmas Day viewing, but said the manner of his exit was down to Fellowes and the show's producers.
Garethe Neame, managing director of the Downton Abbey producer Carnival Films, described Giamatti's character as a "rather free-spirited uncle" and predicted that he and MacLaine would "upset the Granthams' apple cart in this year's Christmas Day episode".
