Line of Duty fans are certain they've worked out who H is after spotting a glaring spelling mistake.
Sunday's dramatic instalment of the BBC crime show ended on an epic cliffhanger after Acting Detective Superintendent Jo Davidson (Kelly McDonald) was revealed as a relative of Tommy Hunter, the leader of the organised crime syndicate.
During a conversation with the anonymous OCG boss, Jo was ordered to "get rid of" Detective Inspector Kate Fleming (Vicky McClure) after two members of the group had been killed during a police operation, reports Wales Online.
In response to the order, Jo said: "As long as it's my last job".
The mystery person then replied: "Definately" - which is exactly how Hastings previously spelt it.
In series five, the anonymous boss made the same mistake during an online conversation with undercover cop John Corbett (Stephen Graham).
When John suggested an armed raid as a depot, the 'Unknown User' said that the heist was “definately high risk”.
Then, Superintendent Hastings himself made the same mistake.
After John Corbett died, the police managed to gain access to the metadata of H which allowed them to impersonate the unknown user and gain contact with the OGC.
But an impatient Hastings took over the conversation and made the same spelling mistake saying he could "definately pull the right strings."
Viewers rushed to Twitter to make the connection, as one person said: "The typo...THE TYPO!!!!!!!"
Another wrote: "PLEASE TELL ME THE ‘definately’ typo was deliberate!!"
"The typo that separates the die-hard fans from the regular fans," said a third.
And someone else put: "Hastings has got to be H! He made the same spelling mistake last season."
When Hastings was eventually suspended from his post and brought in for questioning by AC-3's DCS Patricia Carmichael she asked him if he misspelt the word because he was in fact 'H'.
She said: "Isn’t it more likely that you inadvertently misspelt this word? Isn’t it more likely that you made the same mistake as H because you are H?"
But of course, he denied the accusation.
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