Peter Capaldi knew he was in New York the minute he stepped out of a classic yellow cab that drove him to the premiere of Doctor Who.

"Someone just shouted at me from the crowd, 'The first Italian Doctor'," he said, laughing.

Peter is the 12th actor to play the Doctor in six decades. At 56, he is also the oldest since the first, William Hartnell.

Show runner Steven Moffat is not concerned that younger viewers will be turned off by an older Time Lord.

"Is that why Santa Claus never worked as an old man and kids didn't like him?" he joked.

"Look, I hate to tell you this, but to kids, (previous 31-year-old Doctor) Matt Smith was ancient, right? I mean we're all ancient to them so [I'm] not remotely [worried]."

Steven is also not dwelling on a recent online leak of scripts for several upcoming episodes.

"There's nothing we can do about it. We were a bit depressed about it, especially me - but what can you do," he said with a shrug.

Although the Doctor has changed, his companion has not. Jenna Coleman returns as Clara Oswald, who was also Smith's sidekick.

"They're kind of deeply addicted and bound to each other despite how much they annoy each other," Jenna explained of her character's relationship to the new Doctor.

Peter added: "I think Clara's the only person that can tell the Doctor what to do and he's very bonded to her and has a very deep affection for her, so although she drives him crazy sometimes, he can't stop inviting her to travel with him."

Peter and Jenna have been on a world tour of seven cities across five continents in 12 days to promote the new season, which starts on August 23.