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The sonic screwdriver - Doctor Who's trusty all-purpose tool which has got him out of a few scrapes - is to be replaced for the ninth series of the BBC sci-fi adventure show with sonic sunglasses!

Star Peter Capaldi revealed the brand new accessory for the Time Lord on-set in Caerwent and also confirmed that the Doctor will be having a more relaxed new look in the new series.

"In the Christmas special we were in the Antarctic so I thought I’d better put a hoody on and I quite liked it.

"I thought we’d get some more of those, and started playing around with that. So he’s loosening up a bit more this series, but sometimes he does go back to his more severe look.

"And there are a few trousery things – but that will become clear when you see the show."

I could have been the Doctor Who World Tour last year which prompted the invention of the Sonic Sunglasses, as Capaldi was spotted looking very cool in Cardiff, New York, Mexico and other places in a pair of black Wayfarer-style specs.

"I’ve got sonic sunglass, it wasn’t my idea but I like it, I get free Ray-Bans now. I was just wearing shades because it was sunny, and I was Doctor Who and it looked cool."

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Looking cool in sunglasses wasn't a a burden for Capaldi, but approving a toy of his character wasn't so easy, especially when it came to his hair colour.

"I have to approve toys so they bring me them to look at, and this year there’s a Mr Potato Head coming out, so I had to approve my Mr Potato Head.

" I kept going 'is the hair right? Is it meant to be grey? I still think my hair’s brown but my merchandise has grey hair!"

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The actor's hair has been a talking point during this, his second series in the role of Doctor Who, Capaldi explains: "I’ve always wanted my hair to be longer.

"It always has to be a decisive change in the first series, and Matt (Smith) being so friendly and open they wanted to make a marked difference. It just grows and I’m lucky it’s still there.

"Some people may think I was going for the full Pertwee bouffant, and it’s almost there."

Jon Pertwee is the third Doctor Who and Capaldi's favourite, a longtime fan of the show he not alone on set.

He explains: "I don’t think I’m the biggest fan, the knowledge on set is immense, joking aside it's great that there are so many people who love the show who make it, to be honest I think that’s why it’s been successful.

"It’s made by people who love it and that means they will go the extra mile. There’s a lot of big fans on the show."

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But even for a longtime lover of the show, Capaldi reveals that he is no expert compared with some: " I’ve been told pointedly I’m not a scholar, I think even the word fan is wrong, I think people have individual relationships with Doctor Who that is quite private.

"It’s their own individual take on it and they get their own things out of it , it’s part of my upbringing and it’s very deeply ingrained in me, so I’m not really that bothered about when and where, the trainspotting element of it.

Watch the Doctor Who series 9 trailer:

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But it's that worldwide love of the show which puts Capaldi in awe of what he's involved in:"I think my surprise is the depth of affection at which it is held internationally, that was really a shock, a nice shock.

"All I have to do is walk into a room of people who like Doctor Who and they smile, that wouldn’t happen if I wasn’t Doctor Who.

"It’s easy to surf this tide of affection, I’ve been very lucky people don’t pull me up or tell me they hate me...they keep that to themselves.

"It’s a very privileged position for people to be in. I have a sense of wonder that I’m in that position.

"People smile shout at you and wave at you in the street, I had a little girl come up and throw her arms around my shoulders. It’s so easy, they want so little for you, they want you to be Doctor Who."

See Doctor Who filming in Cardiff in our gallery: