Line Of Duty fans were stunned to learn that hugely popular actor James Nesbitt had been cast as bent copper Marcus Thurwell.
Despite earlier claims that he had been snubbed from the show, fans were finally able to put a face to the former DCI of Central Police when his picture flashed up on a computer screen.
The casting surprise comes during a cram-packed episode full of shocking twists alongside a poignant tribute to the real-life victims of two racially motivated attacks.
So who is Marcus Thurwell?
While there had been a brief reference to the character back in series three, it wasn't until yesterday that the character's image finally surfaced.
The former Chief Inspector is now retired and is believed to be living in Spain, where he was last spotted some years ago.
While the character appears to have stepped away from the force in recent years, it is understood that he was involved with some seriously dodgy dealings while working as the DCI.
Although little is known about the character so far, Thurwell had been linked to the Organised Crime Group while he was working on the force.
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During last night's episode, Steve Arnott was looking into the child exploitation at Sandsview Boys Home, when they learned that Thurwell was sought for questioning as a suspect. The inquiry was dropped after Patrick Fairbank was convicted and imprisoned.
It has also emerged that Gail Vella had been investigating the death of Lawrence Christopher - who died in police custody in 2003 - and even approached the commissioner before her murder.
Thurwell was the Senior Investigating Officer at that time and had a hand in the policing failures that surround the case.
Speaking about James' casting to the show, creator Jed Mercurio has revealed that the actor was told to keep his role top-secret prior to the show.
"It was easier to keep it secret by plotting the scheme between the two of us rather than involving a proper casting process," Jed said.
"I did warn him there were two conditions: One, he'd have to wear shorts which might get very nippy on a cold day in Belfast and, two, he'd have to lie about it.
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