Following the period drama's worldwide success, there have been frequent rumours that Fellowes might take the project to the big screen.
The writer told DS that he thought a Downton film might be "quite fun", but added that if it was up to him, he would wait for the show to end on TV, in the style of HBO's Sex and the City.
Fellowes's series has started 2013 in style, picking up record ratings in the US and taking home prizes at the National TV Awards in the UK and Screen Actors Guild Awards in America.
The show will return for a fourth series in the UK this autumn.
Watch Hugh Bonneville and Julian Fellowes talking about series four of Downton Abbey backstage at the NTAs below: