Last week, 'Line of Duty' showrunner Jed Mercurio teased multiple guest stars for the next season and now we know one of them.

Scottish actor Kelly Macdonald will join the cast as Detective Chief Inspector Joanne Davidson, the senior investigating officer of an unsolved murder whose unconventional conduct raises suspicions at AC-12.

Kelly-MacDonaldKelly MacDonald

Macdonald is best known for her roles in 'Trainspotting', 'Gosford Park', 'State Of Play', 'No Country For Old Men', 'Boardwalk Empire' and, most recently, 'The Victim' and 'Giri/Haji'.

She will start work on 'Line Of Duty' series six when filming begins next year, opposite series leads Martin Compston, Vicky McClure and Adrian Dunbar, who are also confirmed to return.

'Line of Duty' writer and showrunner, Jed Mercurio, says: "We're honoured that Kelly Macdonald will join Martin, Vicky and Adrian in series six of 'Line Of Duty'. DCI Joanne Davidson will prove the most enigmatic adversary AC-12 have ever faced."

Piers Wenger, Controller of BBC Drama, says: “We’re delighted that Kelly Macdonald is coming on board for series six. She’s one of the UK’s most versatile actors and we’re excited for viewers to see what Jed’s scripts have in store for her when she joins the 'Line Of Duty' team."

No word yet on when we will get to see season 6 but we'll keep you posted.