Doctor Who writer Steven Moffat said it felt "like a miracle" when he saw the show's new star Jenna-Louise Coleman audition with Matt Smith.
The 25-year-old former Emmerdale actress was unveiled today as the Time Lord's new assistant in the sci-fi show.
Karen Gillan, who plays Amy Pond, is due to leave the BBC adventure this year along with Arthur Darvill, who plays her on-screen husband Rory.
Moffat said Coleman's partnership with Smith "came to life" during the auditions.
He said: "It always feels like a miracle when you find the right person because we saw a lot of brilliant actresses.
"There was a moment I remember from the second time she came in, and they were auditioning together and they both looked frightened doing a Doctor Who scene, and it just was an instant poster."
Coleman, who played lesbian Jasmine Thomas in the Yorkshire soap, starts filming in May and will make her first appearance in the Christmas Day special.
Moffat remained tight-lipped about the new series, saying Coleman's introduction would not be "the usual story".
He said: "It's a very, very different way for the Doctor to meet his new friend."
Fans will see six episodes this year with eight more in 2013 and Moffat revealed Gillan would be written out in the fifth episode of 2012 in a "final encounter" with the weeping angels.
He said: "Not everyone gets out alive and I mean it this time."
Coleman, from Blackpool, will soon appear as Annie Desmond in Julian Fellowes' new ITV1 Titanic drama.
She said she was "beyond excited" to join the show and "so relieved" to finally be able to tell people she had the job six weeks after finding out.
She said: "I was in Marks and Spencer holding an avocado deciding what goes best in a salmon salad, that was my big debate at the time, and then I got the phone call and just had to put everything down and leave the shop and go for a walk.
"I told my mum but I couldn't tell anyone else so I was this weird excited but had to act completely normal."
Coleman said she knew she wanted the job after the audition process was "so much fun".
She said: "Working with Matt it felt so spontaneous, and we just didn't know where it was going to go and he's got so much energy that's its just infectious, so that's what I feel excited about."
Coleman also revealed that her new role particularly delighted one member of her family - her grandmother.
She said: "It's her favourite, favourite show and she loves Matt as well so to give her the news was really exciting."
