Downton Abbey creator Julian Fellowes has hinted that the next series of the hit show could be its last.
The ITV1 drama, telling the story of the aristocratic Crawley family, is set to return to television screens later this year for a fifth series, having made its debut in 2010.
But Lord Fellowes has now said in an interview that the saga will not "go on forever".
He has been commissioned to write a new American drama called The Gilded Age but told The Wall Street Journal that work on the programme would not start until Downton had come to an end.
Lord Fellowes said: "It's for NBC Universal and it will happen when Downton finishes because I just couldn't do both at once.
"I haven't written it yet, but it's about the old aristocracy, the Winthrops and the Stuyvesants and the new money of oil and gas and shipping in the 1870s. It will all be fiction - it won't be real people - but when those families descended on New York, they took over."
The writer, who is also an actor, reassured fans that there would be a fifth series of Downton but referring to a long-running US courtroom drama, added: "I don't know yet if there is a season six, but it's not going to go on forever. It won't be Perry Mason."
Downton Abbey creator Julian Fellowes revealed he found it "testing" to write Dan Stevens' character out of the series after the actor announced he was leaving.
Viewers who settled down to the Christmas special were shocked when Matthew Crawley was spectacularly killed off - just after his wife Lady Mary gave birth to their first child.
Fellowes admitted to The Hollywood Reporter that after the couple's long love affair, the only way to write him out was to kill him off.
But as Jessica Brown Findlay's character Lady Sybil had died just a few episodes earlier, the Downton creator did not want to dwell on Crawley's death.
"We knew Jessica was leaving from quite a long time before, and so we completely decided calmly to kill her off in the fifth episode, so that would give people three episodes to recover, and then we'd have the Christmas special ... so we had a whole episode of her dying", Fellowes said.
"But having done that, when the news came through that Dan was also leaving we couldn't very well do it again, so that was a bit testing".
The Downton Abbey creator Lord Fellowes has paid tribute to Richard Briers, who has died aged 79.
The pair starred in the BBC comedy drama Monarch of the Glen.
Lord Fellowes told ITV News:
Sangeeta Bhabra from ITV Meridian has interviewed writer Lord Julian Fellowes about the new ITV drama, in which he talks about how the series was made, and how he tried to make everything as authentic as possible.