Line of Duty fans were taken aback as Kate Fleming recognised Ryan Pilkington.
Ryan was back at the Central Police force as a student police officer offering to make a cup of tea to DCI Davidson.
However, DI Kate Flemming spotted him and asked if they had worked before together.
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While Ryan denied knowing Kate, she was left extremely suspicious.
But luckily, eagle-eyed viewers identified Ryan as Ryan Pilkington, who first appeared in Line of Duty in series one.
Karen tweeted: "BOOM!!! And there he is... Ryan has returned."
Seyam said: "WHO ELSE SHOUTED IN ANGER WHEN THEY SAW RYAN."
Roch wrote: "Of course Ryan Pilkington would become a part of the police force."
And Maidy said: "When ya see Ryan Pilkington again...mother of God."
Line of Duty viewers met Ryan back in series one as a young teenager.
He grew up on Moss Heath’s Borogrove Estate and worked for Tommy Hunter.
He collected drugs and debts and delivered burner phones to Hunter's team.
And at one point he tried to cut Steve’s fingers off with bolt cutters.
But Ryan returned in series five as an organised crime gang member - and was responsible for John Corbett's death.
When John revealed himself as a traitor to the Organised Crime Syndicate, Ryan slit his throat when he was distracted.
