The Countess of Wessex has shared her passion for Line Of Duty and revealed she guessed who the mysterious H was before it was revealed in the series finale of the hit show.

The conclusion of the blockbuster BBC series saw DSU Ian Buckells, played by Nigel Boyle, unmasked as the corrupt police officer at the top of a criminal conspiracy.

In an interview with BBC Radio 5 Live ’s Naga Munchetty, Sophie said she deduced the twist ahead of time.

She said: “I was really disappointed in myself for having guessed it. Because I was, yes …  I kept on thinking ‘It can’t be, it can’t be him but it’s got to be. There isn’t any other choice. There is no-one else that it could be’.

“I mean, it wasn’t long before the end. But it was long enough I think.”

Sophie mistakenly referred to the show as Call Of Duty, the popular video game, adding: “I am so bad! I am so bad at remembering the names of anything, whether it comes to books, whether it comes to programmes, films, anything.  I’ll go, ‘Ooh you know that one with what’s his name?’

“I’m so bad at it. I’d never watched it and I started the first episode and that was it, I was hooked.”

The final episode of the series, which aired last month, saw fans and critics split over the reveal, with some saying they felt let down and others praising the decision to avoid a more dramatic conclusion.

It was watched by an average of 12.8 million people, with a 56.2% share in overnight viewing figures, making it the most watched episode of a drama in 20 years, the BBC said.

Martin Compston, who plays Steve Arnott, revealed that he, Adrian Dunbar (Ted Hastings), Vicky McClure (Kate Fleming) and Mercurio had agreed to get “AC12million” tattoos if the show hit the milestone – in reference to the show’s crime-busting AC-12 unit.