Doctor Who actor Peter Capaldi announced he will be stepping down from his role as the Time Lord earlier this year but has just revealed the real reason why.

The 58-year-old star, who hails from Glasgow, Scotland, has made quite the impression as the 12th and current incarnation of The Doctor in the BBC1 sci-fi series. He now claims that his reason for vacating the Tardis is that, as an actor, he was struggling to keep the character interesting.

On playing the same role for a long period, he reflected: "I've never done anything for any length of time.

"Even [political comedy] The Thick of It was only 20 episodes over four years. I'll have done 40 episodes of Doctor Who.

"I don't think if I stayed on I'd be able to think of another way to say, 'This could be the end of civilisation as we know it'.

"I've always gone from one job to the other and seen what was around the corner and I want to get back to that," The Mirror reports.

Capaldi has starred in over 40 films and television shows since his appearance as Danny Oldsen in Local Hero (1983). He has also worked as a director, presenter and writer, directing several episodes of the 2009 BBC Four sitcom Getting on.

Series 10 of Doctor Who will return to BBC1 this Saturday, with Matt Lucas returning as Nardole alongside Capaldi and new companion Bill (Pearl Mackie). Nardole is set to have a secret mission for his comeback, with the Doctor in opener The Pilot.

Joining Capaldi in leaving is show boss Steven Moffat, who will be replaced by Broadchurch creator Chris Chibnall.

Hinting on the actor to play the next Doctor Who, Mackie claimed it's about time the lead role was taken up by a gay character. She claims it is "about time" the iconic sci-fi series featured an openly gay lead: "It shouldn't be a big deal in the 21st century. It's about time, isn't it?" she said.

Potts will reportedly introduce her girlfriend in the first episode of the new series.

"[Being gay] is not the main thing that defines her character – it's something that's part of her and something that she's very happy and very comfortable with."

Doctor Who returns at 7.20pm on BBC1 this Saturday 15 April.