On Tuesday (13 April), visitors to BBC Maestro were able to glimpse a photo of a forthcoming episode, which depicted Detective Inspector Steve Arnott (Martin Compston) looking over a database of characters.
One of the faces visible in the database reportedly belonged to a major actor, whose involvement in Line of Duty had previously not been announced.
A short scene involving the actor was also able to be viewed on the site.
BBC Maestro is a platform on which users can pay for educational video courses by a number of high-profile stars, including Marco Pierre White, Gary Barlow and Line of Duty creator Jed Mercurio.
Mercurio addressed the spoiler flub in a comment to The Sun, joking: “The outstanding detective work of eagle-eyed Line of Duty fans has been awarded a glowing commendation from the gaffer himself, Supt Ted Hastings. Their call-up papers for AC-12 are in the post!”
Speculation over a mystery new cast member joining Line of Duty reached a fever pitch in the wake of Sunday (11 April) night’s episode.
The episode ended with the discovery that DCI Joanne Davidson (Kelly Macdonald) is secretly related to a character presumably known to fans.
Arnott revealed the news to Superintendent Ted Hastings (Adrian Dunbar), and handed him a file featuring the details of a person who is “identified over the page”. Hastings was so shocked by the man’s identity that he dramatically exclaimed, “Mother of God!”
It remains unclear whether Davidson’s relation is a new character, or someone from a previous series of Line of Duty.
A number of possible suspects have been speculated about online, while a plot description for the next episode in the series has teased a “potentially dangerous situation” for AC-12. Newly released photos for episode five appear have fuelled recent rumours.
The Independent has reached out to BBC Maestro for comment.
Line of Duty continues at 9pm on Sunday on BBC One.
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