"I did test after test including a screen-test where Ken played the prince, and he was amazing. And then I waited a month to find out whether I had the role. Then one day Ken rang me while I was on set for Downton. He said, 'I want you to be my Cinderella'. I screamed and Michelle [Dockery] and Laura [Carmichael] ran over to me but I wasn't allowed to tell anyone."
Explains director Kenneth Branagh: "It was Lily's voice, it was her warmth and her sense of humour. She has a combination of gentleness and strength, plus she's a beautiful, beautiful girl and has a lovely heart and that comes through her work.
"I was aware of Lily and liked very much what she was doing in Downton Abbey. She has had incredible training in front of the camera inside an amazing company of actors. She was in a master class on a daily basis in front of Maggie Smith, Penelope Wilton, Phyllis Logan and, of course, Jim Carter and Hugh Bonneville, and it shows."
So enamoured is he of the Downton cast that he also chose Sophie McShera, who plays kitchen maid Daisy Mason, to play Drizella.
"Oh, Sophie loved the chance to boss me around for a change," says James of the reversed upstairs-downstairs dynamic.
"I wouldn't have got this role without Downton," she acknowledges. "But being on the show hasn't changed my everyday life in the way you might imagine because I'm not recognised that often."
Trailer: Disney's Cinderella
In an interview with the Independent, she said, "I think I'm quite chameleon-y. I look quite different on camera to how I look in the flesh. Some people have such unique faces or such a strong look you can't help but notice them. I don't think I'm really like that."
Born Lily Thomson but forced to take a stage name because of another actress with that name, James comes from an acting family and much of her pre-Downton career was spent on stage.
Unsurprisingly, James was excited to work with Cate Blanchett, at her best in Cinderella as the deliciously wicked stepmother.
"She's always been my favourite actress," she gushes. "She exceeded every expectation when I met her. She's the coolest, funniest and most intelligent woman, and to act with her was incredible. She forces you to be in the moment because she's so alive. I learned a lot just by being with her." She giggles. "I just love her."
James says playing Cinderella influenced her on a personal level.
"I hope this isn't cheesy but while we were filming, I felt like a stronger person playing her. I felt really confident because there was an openness to her and such strength. To have courage and be kind is such a simple message but I began to apply it to myself. I feel it's really profound and I hope to be more like her in the future after playing the role."
Well on her way to a formidable career, James is busy with two high-profile projects, each with a literary element. First is War and Peace made for television. "It's one of the biggest-scale things the BBC has ever done. I'm playing Natasha, and though it's a great experience, it's also a little scary," she admits. She will follow War and Peace with the quirky Pride, Prejudice and Zombies, the Jane Austen horror parody that also stars former Doctor Who actor Matt Smith, whom she is dating.
"It was so much fun after Cinderella to play someone whose strength comes from fighting. It's all about slaying zombies and being a badass action hero."
Who: Lily James in the title role of Cinderella, directed by Kenneth Branagh and also starring Cate Blanchett and Helena Bonham Carter
When and where: Opens at cinemas on Thursday, March 26
- TimeOut
