New 'Doctor Who' companion Pearl Mackie never thought about filling Jenna Coleman's shoes on the show - because she didn't want to "freak out".

Pearl Mackie as Bill Potts

Pearl Mackie as Bill Potts

The 29-year-old actress is joining Twelfth Doctor Peter Capaldi and Matt Lucas as returning character Nardole in the TARDIS for the upcoming new series as plucky Bill Potts.

Peter's last co-star was the much-loved Jenna Coleman - who played Clara Oswald in three series, beginning her tenure with Eleventh Doctor Matt Smith and leaving in 2015 - but rather than think about her predecessor Pearl wanted to focus on bringing her own unique performance to the BBC sci-fi show.

Speaking at a Q&A attended by BANG Showbiz to launch the new series in London on Tuesday night (04.04.17), she said: "I think one of the greatest things about Doctor Who is that with each companion you get a different story and a different insight into the Doctor. I didn't look at it as taking over from Clara, who is her own companion, her own entity, I just looked at it as a really nice treat to get to work with Peter and all the other people. I've just had a great time really. I haven't looked at it as filling anyone's shoes which is probably good otherwise I'd have freaked out. That would have been pretty scary."

Pearl admits she was very nervous when she auditioned for the part of Bill, and her tension was increased when she got to do a read through with Peter, 58, before being offered the role by showrunner Steven Moffat.

She said: "It's mad to join the show, it's such a rollercoaster I'm still trying to get my head around it, I can't believe I'm in Doctor Who. I only did two reads and the second one we did together that was brilliant, the first one I did with a computer that did a really weird Peter Capaldi impression. It's so rare to get to do a read through with your co-star, so I had to remind myself to do proper acting."

Although she readily confesses to being a bundle of nerves, Moffat knew he'd found his new companion in the first few minutes of her audition.

He said: "She was the first person though the door. All the other people who came trough were terrifyingly brilliant but Pearl was marvellous, me and Peter were like, 'Well what do we do now?' She says she was nervous but I think she was lying. We were all sat there like awkward middle-aged men wondering what to say. Pearl was wonderfully accomplished and I thought, 'Wow, aren't young people are grown up now.' She didn't look nervous at all."

'Doctor Who' returns to BBC One with 'The Pilot' on April 15, 2017.