Unsurprisingly, it hasn't taken the show's fanbase long to play detective and propose a range of guesses as to the identity of Jo Davidson's mystery relative, but former star Craig Parkinson has already shot down one fan theory.
Replying to a fan's suggestion that his old character Matthew 'Dot' Cottan could be the family member in question, Parkinson responded, "Yeah, it isn’t."
Parkinson, who currently hosts the Obsessed with...Line of Duty podcast for BBC Sounds, played bent copper Dot on the first three seasons of the show until he was killed off in the dramatic series three finale.
He has said he's frequently asked by fans if Dot could make a return to the show in one form or another but has always maintained that he won't be coming back.
As for the real identity of Jo's relative, several names have been put forward by sleuthing fans, including those of Tommy Hunter and John Corbett.
Tommy – the OCG boss who was introduced in series one – has been suggested partly due to his and Jo's shared Glaswegian heritage, while fans had previously noted that a photo of Jo's mum looked eerily similar to former undercover cop Corbett’s birth mother, Anne-Marie McGillis.
Explaining the situation to Ted Hastings at the end of the episode, Steve Arnott revealed that DNA deposits detected at Farida Jatri's house were compared against the whole system, and "the analysis detected partial matches to a nominal whose DNA is stored on other police databases".
It is unclear if this relates to another police officer, or simply a criminal whose information was stored on the Central Police Force's databases but fans will already be counting down the days until the next episode when they can find out.