Siobhan Finneran as O'Brien in 'Downton Abbey'

Siobhan Finneran has played Lady Grantham's cunning maid Sarah O'Brien on the ITV period drama since it began but has confirmed she will not appear in season four.

She told "I'm not doing any more. O'Brien is a thoroughly despicable human being - that was great to play."

According to TVLine, her exit will not be shown onscreen and is expected to take place during the six month time jump between the end of season three and the beginning of season four.

However, the character will not be killed off, leaving open the possibility of a return.

Siobhan is just the latest star to leave the hugely popular series, Dan Stevens, who played Matthew Crawley, and Jessica Brown Findlay, who starred as Lady Sybil, both left the series after their characters were killed off last season.

Producer Gareth Neame recently insisted Dan's departure would turn into a “great opportunity” for his onscreen wife Lady Mary Crawley [Michelle Dockery].

He explained: "This is a lesson in something that seems like a really big loss in the moment [that] will actually turn into a great opportunity [for Lady Mary], which it will also be for the show, to take a turn in a whole different direction."