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Sunday evening's episode of Line of Duty left fans reeling, especially when it was revealed that Jo Davidson (Kelly Macdonald) is related to Tommy Hunter.
But some eagle-eyed fans have spotted a shocking detail about the truth behind their relations, after honing in on a post-it note shown during the episode.
Viewers took to Twitter after noticing the clue, which seems to claim Jo is both the niece and daughter of Tommy.
Posting a screen grab of the post-it on Twitter, one person said the note read: "Jo Davidson's DNA has been identified at Farida Jatri's house. A match has been made to TOMMY HUNTER, stating she is both his niece and daughter."
Another said: "In case anyone missed the homozygosity reference in @Line_of_duty it basically means Jo Davidson is both Tommy Hunter's daughter AND niece."
And another tweeted: "Hang on hang on, jo is tommy hunters niece and daughter????"
Along with the clue, there were previous references to the pair's DNA results during the ep, when Steve Arnott (Martin Compson) told Kate Fleming (Vicky McClure) that there was a match, explaining there was "homozygosity in their DNA".
According to Medicine Net, 'homozygosity' is 'the state of possessing two identical forms of a particular gene, one inherited from each parent'.
Basically, it indicates Jo and Tommy are very closely related, and considering the post-it clue, could even suggest incest.
Sunday's episode also delivered the ultimate cliffhanger, with Kate facing off against cop-killer extraordinaire Ryan Pilkington (Gregory Parker) after being lured to a lorry park by Jo.
With both Kate and Ryan aiming their guns at one another, the screen goes black - and we hear two shots fired, before the credits roll (and the audience are left in the dark about who survived).
While we've got everything crossed that Kate survives, actor Vicky McClure did seem to suggest that Kate could be killed off this series.
"Every episode of Line of Duty history is terrifying and [writer] Jed [Mercurio] is always there to serve the story - it is exactly what happened with Dot," she told Craig Parkinson on the Obsessed With...Line of Duty podcast.
"Dot's time came when it was right to serve the story and that is what Jed will always do. I don't want to put everything out there but Jed serves the story."
Line Of Duty continues on Sundays at 9pm, on BBC One - and we've got a feeling this week's will be an unmissable episode...
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