Christopher Nolan had no idea how famous Harry Styles was when he cast him in 'Dunkirk'.

Harry Styles in Dunkirk

Harry Styles in Dunkirk

The 46-year-old director knew Harry was in boyband One Direction when he auditioned for a part in the upcoming movie but admitted he was unaware of exactly how big of a star Harry is before he started working with him.

He said: "I don't think I was that aware really of how famous Harry was. I mean, my daughter had talked about him. My kids talked about him, but I wasn't really that aware of it. So the truth is, I cast Harry because he fit the part wonderfully and truly earned a seat at the table."

And Harry's Oscar winning co-star Mark Rylance revealed working with the 'Sign of the Times' singer impressed his niece more than anything else in his career to date.

He said: "She was just more excited than anything I've ever done because I was going to be acting with Harry Styles. I went up in her estimation. I won the Harry!"

Harry, 23, revealed his One Direction bandmates - Niall Horan, Liam Payne and Louis Tomlinson - are excited about his big screen debut.

He said: "They are big fans of Chris, too, and I think they're excited to see it."

But he admitted he was shocked by the large-scale production during his early days on set.

He explained: "I'd say seeing the scale of the production was very overwhelming. I think whatever you imagine kind of a giant film set to be like, this was very ambitious even by those standards. You know the boats and the planes and the volume of bodies ... it was pretty amazing."

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