LOS ANGELES • Director Christopher Nolan's children think he is super cool after they learnt that the cast of his World War II movie, Dunkirk, includes One Direction singer Harry Styles.

"My kids talked about him, but I wasn't really that aware" of Styles' fame, the director was quoted by Hollywood Reporter as saying.

"So the truth is, I cast Harry because he fit the part wonderfully and truly earned a seat at the table," he added.

The movie also stars acclaimed actor Mark Rylance, whose 11-year- old niece, he said, was "more excited than anything I've ever done because I was going to be acting with Styles".

"I went up in her estimation," he said.

This, despite the fact that Rylance has won an Oscar for Best Supporting Actor for his role in Bridge Of Spies (2015).

Styles, 23, portrays a British soldier in the thriller about the evacuation of more than 300,000 Allied soldiers from Dunkirk, France, in 1940 after they were trapped by the German army.

Writing in The Telegraph, Nolan said: "I also think it's a universal story - about the individual drive for survival. And the fundamental concept of a desperation to get home."

Dunkirk is set to open next Thursday in Singapore and next Friday in North America.