After weeks of speculation, relatively unknown actor Matt Smith has been cast as the 11th Doctor Who.

Smith will replace David Tennant at the helm of the Tardis, and is due to first appear on our screens as the revered doctor in 2010.

Smith, 26, is the youngest ever doctor and has appeared in Alan Bennett's play The History Boys at the National Theatre in London, and alongside Christian Slater in Swimming with Sharks in the West End.

He said he was delighted to take on the role.

Smith explained: "I've got this wonderful journey in front of me. I've got six months to build this Time Lord and that's such an exciting prospect.

"I'm just so excited about the journey that is in front of me. It's a wonderful privilege and challenge that I hope I will thrive on."

He added: "I feel proud and honoured to have been given this opportunity to join a team of people that has worked so tirelessly to make the show so thrilling.

"David Tennant has made the role his own, brilliantly, with grace, talent and persistent dedication. I hope to learn from the standards set by him.

"The challenge for me is to do justice to the show's illustrious past, my predecessors, and most importantly, to those who watch it. I really cannot wait."

Tennant announced in October last year that he would be stepping down from his role as the doctor at the end of this year.

The fifth series of the much-loved sci-fi hit will also have a new lead writer and executive producer with Bafta award-winning writer Steven Moffat taking over from Russell T Davies.

Moffat will be joined by Piers Wenger, who will be the new executive producer for BBC Wales making the show.

Wenger, head of drama at BBC Wales, added: "With two hearts, a ferocious mind and over 900 years of experience behind him, it's not every 26-year-old actor who can take on a role like the Doctor but within moments of meeting Matt he showed the skill and imagination needed to create a Doctor all of his own.

"It's just the beginning of the journey for Matt but with Steven Moffat's scripts and the expertise of the production team in Cardiff behind him, there is no-one more perfect than him to be taking the Tardis to exciting new futures when the series returns in 2010."

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