The actor revealed as Line Of Duty’s mysterious "H" has said he was "buzzing with excitement" on finding out his character was the talked-about figure.
During Sunday night’s finale of the BBC One series, DCI Ian Buckells, played by Nigel Boyle, was unmasked as crooked police officer H.
Mr Boyle, who grew up in Birmingham, said: "I was buzzing with excitement! I never suspected it because I know how Jed (Mercurio) leads people down the garden path with really good red herrings, so I didn’t really pay too much attention to things like Buckells’ golf clubs etc, but clearly I should have done!”
“I’d fully bought into the idea that Buckells was low on competence levels but looking back it all makes sense!” he said.
Speaking about finding out his character was "the fourth man" - an individual leading a network of corrupt officers behind the murder of journalist Gail Vella - Mr Boyle said the show’s creator Mr Mercurio shared the news in a phone call.
"We’d had the first four scripts and started filming some of series six when we had to stop due to the first lockdown,” he explained.
“When we were about to resume filming, Jed sent me a text saying, ‘Are you free for a chat at some point today? Don’t worry it’s not that call...’
"Which I took to mean that I wasn’t going to end up dead! But I was still quite nervous and not sure what he wanted to talk to me about.
"He called me and said, ‘The scripts for the next episodes are going to be sent out imminently and so it’s time to tell you the secret that I’ve been keeping, you’re going to be revealed as someone rather significant..."
Mr Boyle has been in Line Of Duty since the first series of the police drama which aired in 2012.
The actor, who also starred in Peaky Blinders, said the only person he told about being H was his wife, Lainy.
He said: "I’ve been sitting on it for a long time! The only person I told was my wife, nobody else, I know how much is at stake.
“Even if you tell someone you trust with your life, they might tell someone they trust with their life and then suddenly more and more people know. When friends have asked me who H is I’ve just said there isn’t an H."
The final episode of the sixth series was watched by an average of 12.8 million people, with a 56.2 per cent share in overnight viewing figures, the BBC has said.
The episode had a peak viewing figure of 13.1 million, according to the corporation.
Charlotte Moore, the BBC’s chief content officer, said: "Addictive event television, Line Of Duty has kept the nation guessing for the last seven weeks, so it’s no surprise that last night’s jaw-dropping finale set a ratings record.
"Jed Mercurio is a master of his craft, and I would like to congratulate him and the entire cast and crew for delivering such an incredible drama series. I’m looking forward to having a conversation with the team about where we go next and what the future of the series might be."
Additional reporting by PA Media