Oscar-nominated US actor Paul Giamatti is to join the cast of ITV's Downton Abbey, starting with the Christmas episode, it has been announced.
He will star alongside Elizabeth McGovern as Harold, the "maverick, playboy" brother of Lady Grantham.
Dame Kiri Te Kanawa and EastEnders actor Nigel Harman are also set to star in the fourth series of the drama
The stately series was the most-watched drama of 2012, averaging 11.9 million viewers per episode.
"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," said Gareth Neame, from production company Carnival Films.
"We can't wait to see him work alongside Shirley MacLaine, who are both sure to upset the Granthams' apple cart in this year's Christmas Day episode."
The influx of US actors to the period drama reflects its growing popularity in the States.
12.3 million Americans tuned in to finale of series three on 17 February, making it the highest-rated show of the day, and breaking the viewership record for broadcaster PBS.
The show has won nine Emmys, and recently cropped up in summer blockbuster Iron Man 3.
Giamatti had supporting roles in films such as Saving Private Ryan and The Truman Show before his breakout role in wine-tasting romcom Sideways.
In 2008, he won Emmy and Golden Globe awards for his role as former US president John Adams in the drama of the same name.
He was also nominated for a best supporting actor Oscar for his work opposite Russell Crowe in Cinderella Man in 2006.
The Actor is currently filming The Amazing Spider-Man 2, where he is playing The Rhino opposite British star Andrew Garfield.