Neil Patrick Harris had 'never heard' of Doctor Who

Russell T Davies has revealed Neil Patrick Harris was completely unaware of Doctor Who when he was offered a part on the show.

The How I Met Your Mother actor is set to guest star on the long-running science-fiction programme for an upcoming 60th anniversary special episode, The Giggle.

"He'd never heard of it in his life, bless him," the Doctor Who showrunner remarked of Neil to Entertainment Weekly on Thursday. "I was lucky enough to work with the great man on a show called It's a Sin, about the AIDS crisis in the 1980s, and working with him was such a joy."

Davies continued, "If you go through agents, they often tell you to go away. I was able to send just a text saying, 'Do you fancy reading this?' He read it and literally phoned me up going, 'Let me get this right, so the Doctor's an alien, right?'"

"I was like, 'Oh my god, you really have never heard of Doctor Who!'" Davies recalled. "But he couldn't resist it, and he came to Cardiff, and we had the most spectacular time."

In the upcoming episode - the final of three that have seen the return of David Tennant and Catherine Tate as the Doctor and his companion - Neil plays the Toymaker; an enemy of the Doctor who first appeared on the show in 1966.

"The Toymaker, he's kind of the god of games, so he shuffles cards, he does magic tricks, and all of that fits Neil Patrick Harris," Davies noted of the former Doogie Howser, M.D. child star.

The Giggle airs on BBC One on Saturday 9 December.