Harry Styles found shooting 'Dunkirk' "physically really tough".
The 23-year-old singer makes his acting debut in director Christopher Nolan's upcoming wartime saga and loved working on the "ambitious" film.
He told Rolling Stone magazine: "The movie is so ambitious. Some of the stuff they're doing in this movie is insane. And it was hard, man, physically really tough, but I love acting. I love playing someone else. I'd sleep really well at night, then get up and continue drowning."
The 'Sign of the Times' hitmaker cut off his long, curly locks for the role and previously admitted he felt "naked" with his shorter do.
He recently said: "I felt very naked. When I first told my parents I was going to be in a World War II film, they thought that I was playing a lady on the train station waving the soldiers off, so we had to make the chop. But it was good! It's very breezy."
Meanwhile, director Christopher also spoke about why he offered Harry the role, and said the previously insisted the One Direction hunk had to audition for the movie, just like "thousands" of other hopeful actors.
He revealed: "When we put the cast together, we had some established names. But for the guys on the beach, we really wanted young unknowns. He's not that unknown, but he'd never done anything as an actor before. So he auditioned. I auditioned literally thousands of young men with different combinations of young men. And he had it."
The 46-year-old director previously said the movie - which features an impressive ensemble cast rounded out by the likes of Oscar-winner Mark Rylance, 'Taboo' star Tom Hardy, 'Peaky Blinders' hunk Cillian Murphy and Sir Kenneth Branagh - will transport viewers into the heart of the the British-led rescue mission in 1940 in which 330,000 Allied troops were rescued from the clutches of the Nazis.
He said: "I wanted to tell the story in the most visceral way possible, I wanted to take that audience and put them on that beach.
"At its heart, it's a survival story. The enemy is closing in on the British on this beach with no escape. I wanted to put the audience in the story."
'Dunkirk' is scheduled to hit cinemas in July.