Dame Kiri among new faces at Downton Abbey

Downton Abbey will play host to a number of new faces in season four, including New Zealand soprano Dame Kiri Te Kanawa as well as a drunk, a gentleman with 'history' and the show's first black character.

A new character arrives ... Jessica Brown Findlay as Lady Sybil and Allen Leech as Tom Branson in Downton Abbey

The show will also introduce a black character in the coming season as part of a storyline about race relations in the 1920s.

Casting notes were sent out to actors' agents last month for the role of musician Jack Ross. The description given for Ross is “Male, 25-30. A musician (singer) at an exclusive club in the 20s. He's black and very handsome. A real man (not a boy) with charm and charisma.

The first Christmas special we did of Downton, it was pretty Christmassy. It was the proposal, which was very nice. But that isn't particularly the tradition of these Christmas shows here. In a way, they're supposed to be more dramatic than an ordinary episode of the series.

“Overall he should be a very attractive man with a certain wow factor.”

Ross is expected to be a key character in the fourth series, and should add to the musical mix as “ideally be able to sing brilliantly”.

Executive producer Gareth Neame said "Downton Abbey has seen many great characters visit the house over the years and we couldn't be more thrilled to welcome the new faces that will be joining the regular cast of Downton in series four.

Oscar winner Shirley MacLaine, will also reprise her role as Martha Levinson, the Dowager's nemesis and mother to Cora (Elizabeth McGovern) for the feature-length Christmas special at the end of season four.

Levinson was introduced in the first episodes of season three and was a big hit with fans.

Two major characters will depart over the course of season three, with another destined to disappear between seasons.

Siobhan Finnerman, the actress who fans have grown to love (or to love to hate) as scheming maid Sarah O'Brien, will not return for season four.

Finnerman, 47, told Britain's Daily Mirror: “I'm not doing any more. O'Brien is a thoroughly despicable human being - that was great to play.”

The actress has landed a role in new series The Syndicate, in which she will play a nurse who wins a share of a multimillion-pound Lottery jackpot.

“It is nice to play someone the audience is willing on,” Finnerman said. “Watching the first episode, I was delighted to see how many times I smiled. It's great for the story that starts to unfold. And there's no wig and no corsets, which is good.”

She may not have entirely untangled the corset strings, however, as a spokesperson for Downton Abbey said of the departure: "O'Brien is leaving to do something else, but the door for her character is open."

The foundations for O'Brien's exit are laid in the show's Christmas special and come swiftly on the heels of those of Lady Sybil (Jessica Brown Findlay) halfway through season three (in an episode to air this Sunday in Australia), as well as Matthew Crawley (Dan Stevens).

Stevens has a role in the forthcoming Julian Assange biopic The Fifth Estate, while Findlay has a role in new British series Labyrinth.

The three actors' departures will carry varying degrees of finality, giving weight to comments Fellowes made in an interview with The New York Times regarding writing characters out of the series.

“When an actor playing a servant wants to leave, there isn't really a problem,” Fellowes said. “[The character] gets another job. With members of the family, once they're not prepared to come back for any episodes at all, then it means death.

“So we didn't have any option, really. I was as sorry as everyone else.”

Fellowes acknowledges that the potentially depressing nature of the Christmas special is always likely to be a surprise for international markets.