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Line of Duty fans are convinced that DCI Joanne Davidson (Kelly Macdonald) is related to a character from a past season.
Viewers have taken to Twitter to share their theories after that latest episode, which revealed that Davidson was a blood relative of someone known to AC-12.
You can watch it back here:
But just who could it be?
In the latest episode, shown last night on BBC One, DI Steve Arnott (Martin Compston) and DC Chloe Bishop (Shalom Brune-Franklin) took a file to boss DCI Ted Hastings (Adrian Dunbar), which revealed some vital information.
When Hastings opened the file, Steve revealed that Joanne Davidson was related to someone, presumably from the OCG.
Or could it be that the bent copper is related to John Corbett (Stephen Graham), as some viewers have guessed?
A glimpse of the inside of the file was then seen before the credits rolled, leading viewers guessing as to who it is that Joanne is related to.
And one Twitter user has a theory that could turn out to be correct.
Twitter user @tbuckleythinks believes that Jo Davidson could be related to Tommy Hunter, a leader of clandestine organised crime syndicate.
"I think it will help more to check the DNA sheets when Steve Arnott first sees them, you only get a few seconds in real time but I think it lists names of Joanne Davidson & JOHN THOMAS HUNTER the full name of Tommy Hunter.
"If so then brother/sister is the link."
Hunter also has links to Ryan Pilkington back in the first series, when he gets young Ryan to deliver a burner phone to and threaten Wesley Duke.
So could he have placed Ryan in the police station?
Only time will tell.
Line of Duty airs on BBC One on Sunday evenings at 9pm.
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