Dunkirk: Christopher Nolan says casting Harry Styles was like 'making Heath Ledger the Joker'

'As a director, I have to trust my instincts and my ability to figure out who's the right guy for the part'

Anyone looking at Harry Styles' casting in Dunkirk may be led to believe it was all some kind of promotional stunt - get a winsome pop star to appear in your (admittedly slightly risky) British war epic, and rake in a guaranteed audience.

However, director Christopher Nolan is prepared to defend his decision to the very end, even comparing his move to cast Styles, as one of the young soldiers trapped on the beaches of France during WWII's Operation Dynamo, to his initially controversial choice of Heath Ledger as the Joker.

Of course, Ledger swiftly managed to prove the doubters wrong, which is clearly what Nolan is hoping for with Styles' inclusion in Dunkirk.

"As a director, I have to trust my instincts and my ability to figure out who's the right guy for the part," Nolan told Entertainment Tonight. "What I was seeing [in Styles] was a very charismatic guy, but who clearly had truthfulness and subtlety in his ability to perform as a film actor."

"When I cast Heath Ledger as the Joker it raised a lot of eyebrows and caused a lot of comment," he added. "I have to trust my instincts, and Harry was perfect for this part. He pulled it off with incredible grace and reality."

Indeed, Nolan has stated he didn't even quite grasp how famous Styles was when he cast him, telling The Hollywood Reporter: "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."

Dunkirk follows individuals caught up in the Dunkirk evacuation of May and June 1940, in which 338,226 soldiers were rescued from the beaches of France after being surrounded by the German army.

Dunkirk hits UK cinemas 21 July.