Image caption Peter Capaldi's 12th Doctor with new companion Bill Potts, played by Pearl Mackie

Peter Capaldi has said whoever replaces him in Doctor Who - whether a man or woman - will be "wonderful".

Speaking at a preview of the first episode of his final series on the BBC show, he admitted he'd be "very sad" to say goodbye to the programme.

The story - titled The Pilot - introduces the Doctor's new companion Bill Potts, played by Pearl Mackie.

It sees the Doctor, Bill, and Nardole, played by Matt Lucas, battling a shape-shifting alien across time and space.

Capaldi, 58, who took over the Time Lord role in 2013, announced in January that he would leave the show in the 2017 Christmas special.

Speaking to an invited audience at the screening in London on Tuesday, Capaldi said: "It's an incredible thing to wake up in the morning and go 'Oh, I'm still Doctor Who!' and go and blow up some monsters - and that's how you spend your day.

"When you walk around, people don't see Peter anymore - it's Doctor Who they see - and he gets many more smiles than I do. It'll be sad to say goodbye to him."

Image caption The new Tardis crew: Pearl Mackie, Peter Capaldi and Matt Lucas

Asked about who might take over his role, the Scottish actor chose his words carefully.

"I'm sure whoever that person is will be wonderful," he said.

"Doctor Who is a wonderful part, and they are going to make - if they haven't already done so - a wonderful choice, whether that's a man or a woman."

Speculation has been mounting over who will take over the role, with Fleabag's Phoebe Waller-Bridge among the bookies' favourites.

'Big fuss'

Doctor Who showrunner Steven Moffat said after the screening that he was surprised at the "fuss" over Bill's sexuality.

Last week it was revealed that Mackie's character would be the Time Lord's first openly gay companion.

"We are not expecting any kind of round of applause or pat on the back for that," Moffat said. "That is the minimum of representation you should have on television. The correct response would be: 'What took you so long?'"

"It is important we don't make a big fuss of this in a children's show that communicates directly with children.

"You don't want young kids who regard themselves as boring and normal and happen to fancy their own gender, we don't want them to feel as if they are some kind of special case."

Addressing journalists in the audience, he added jokingly: "It is not your job to frighten children - it is my job!"

Image copyright BBC/BBC Worldwide/Shutterstock Image caption The new series begins on Saturday 15 April

Capaldi said he enjoyed the fact that the Doctor was seen "grounded" on Earth as a university lecturer in the opening episode.

"I loved being at university," he said. "I love it when Doctor Who roots itself in something recognisable and normal."

Doctor Who returns on BBC One on Saturday 15 April.

Follow us on Facebook, on Twitter @BBCNewsEnts, or on Instagram at bbcnewsents. If you have a story suggestion email entertainment.news@bbc.co.uk.