Christopher Nolan says he did not know how famous Harry Styles was before Dunkirk (world war 2)

Soldiers from Britain, Belgium, Canada and France fight against the German Army on the beaches of Dunkirk during the early stages of world war 2.
 Nolan discussed his decision to select Harry Styles of One Direction fame for a part in Dunkirk with Entertainment Tonight Sunday. Though he says he was "new" to Styles, the singer's personality increased Nolan's confidence in Styles' acting ability. What I was seeing was a very charismatic guy, but who clearly had a truthfulness and subtlety in his ability to perform as a film actor," Nolan said.
He also mentioned that his decision to cast Heath Ledger as The Joker in The Dark Knight came as a surprise as well.I have to trust my instincts, and Harry was perfect for this part," Nolan said. "I think he pulled it off with incredible grace and reality.