Matt Smith is to make a cameo appearance in upcoming drama 'An Adventure in Space and Time' - all about the creation of 'Doctor Who'.
The 31-year-old actor, who plays the Eleventh Doctor, appears in the programme just as First Doctor William Hartnell - portrayed by David Bradley - films his final ever scenes in the iconic role.
'An Adventure in Space and Time' creator Mark Gatiss admits he wanted to have the two Doctors in the show to honour Doctor Who's incredible legacy in its 50th year.
Speaking at a screening of the 90-minute programme at the BFI in London, Gatiss told the audience: "There were certain parts of this that I've been thinking about for years. I always knew that I wanted to start on the day of Hartnell's regeneration and use the TARDIS as a flashback device - because you can't get a better one!
"But then I had this idea, wouldn't it be wonderful if Bill looks across the console and sees Matt - the Doctor!
"It's about his legacy, to literally look into the future and say, 50 years later, 'I'm still here.' "
Although the two Time Lords appear on screen they couldn't actually shoot their scenes together because Matt was busy filming the 50th anniversary special, 'The Day of the Doctor'.
And Mark has joked the drama can now be updated so it can be screened every year.
He said: "Because Matt wasn't actually there we can now drop in any Doctor we want. It can be shown every November!"
Mark was joined at the screening and Q&A by David, his fellow cast member Sacha Dhawan - who portrays original 'Doctor Who' director Waris Hussein - Hartnell's granddaughter and biographer Jessica Carney and director Terry McDonough.
Jessica was so moved by 71-year-old David's portrayal of her grandfather she was reduced to tears at the screening.
She said: "It was strange, nerve-racking, all sorts of emotions. I'd like to thank Mark for writing a wonderful show. And I'd like to thank David Bradley for playing my grandfather so well. He really captured the essence of him."
'An Adventure in Space and Time' airs at 9pm on BBC Two on Thursday November 21.
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