Before The Fall first aired in 2013, Jamie Dornan was very much known as a Calvin Klein model and one time other half of Keira Knightley. And then came along Paul Spector. In The Fall, Dornan plays a bereavement councilor (of all things ) and family man who, in his spare time, liked to strangle pretty brunettes. What made writer and director Allan Cubitt take a chance with Dornan in such an unexpected role? 'It’s true, Jamie hadn’t done a massive amount and there were other names floating about, but I was absolutely convinced [by his performance] that we had our Spector,' he has said.

'I for very vociferous about it and said [to the BBC] "If Jamie’s not in it, then we don’t have anyone." And then I sent the tape off to Gillian (who was already cast) and said, "I think we’ve found our Spector," and emailed back to say, "Hoorah…we absolutely have."'

Since then, The Fall has become BBC2’s most watched drama in over a decade. So how does Dornan feel about saying goodbye to the character he has played for four-and-a-half-years? 'Bereft,' he has admitted. 'Maybe it’s an odd word to use but Paul Spector has been a massive part of my life for a long time. He’s completely in my blood. I’m going to miss playing him.'

Part of Cubbitt’s insistence that Dornan was so right for the part was Dornan’s idea that Spector should be portrayed as a loving family man, despite his psychopathic tendencies. 'It seems strange to me now that I felt some sympathy for Paul. Well, maybe not sympathy but I felt like I understood him. I always maintained he had a certain level of love for his kids. But having two kids myself (he has two aged two and six-months with wife Amelia Warner) changes your perspective on things. Life seems more precious than before.'

He can reveal a little of what we can expect in series 3 of The Fall. 'Allun and I talked from a long way out about where the story would go, so I’ve seen the end coming from a long way off. And I’m pretty satisfied by it.'

Gillian Anderson has said she would like to play DC Stella Gibson again at a later date. So would it be weird watching the show without him in it? 'I admit it would make me feel a little sad but I’d definitely watch it. I’d probably get a job as a runner, or make people tea, just hang out.

'It’s a job that means a lot to me and the mainly Irish crew who have become family over four-and-a-half years. On the other hand, not have to inhabit the mind of someone so horrific will maybe be a bit of a relief.'

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The Fall returns to BBC2 at 9pm on Thursday 29 September