The fate of the show lies in the hands of writer and creator Jed Mercurio.
There was a blink-and-you'll-miss-it moment going back as far as series one.
We're still in for a bit of a wait before the prequel debuts, though.
The drama's creator did not hold back after one social media user branded Line Of Duty a "cheap little show".
The police drama's conclusion has sparked a lot of conversation on social media.
Line Of Duty’s First Series Had A Major Clue About The Identity Of The Fourth Man, But Did You Spot It?
Writer Jed Mercurio had planted a hint in the 2012 series but it passed the show’s armchair detectives by.
The Steve Arnott actor said he “fully understood” that the conclusion “wasn’t the 'urgent exit’ type ending some anticipated”.
Missing Line Of Duty already? We might be able to help.
Fans are united in their love of AC-12's unsung hero.
"If everyone has their own ideas and theories, then someone’s not going to be happy somewhere along the line."