Harry Styles has admitted he had "no idea" what he was doing as he made the move from musician to actor for Second World War film epic Dunkirk.
The One Direction star cut off his long curly hair to play a soldier in Christopher Nolan's film of the 1940 evacuation - and escape from Hitler's forces - of hundreds of thousands of British and French soldiers.
Speaking to Dermot O'Leary on BBC Radio 2's Saturday Breakfast, Styles said: "It was one of the best experiences of my life.
"Honestly it was amazing, it was a real challenge.
"I mean, I really loved being the new guy. I loved kind of being so far out of my comfort zone."
He added: "It felt really good to kind of have no idea what I was doing for a little bit."
In an early trailer for the film, which opens in the UK in July, Styles was shown submerged under water in a lifejacket and sitting helplessly on the French beach.
He has now returned to music and debuted the first single of his upcoming debut solo album, Sign Of The Times, on radio on Friday.
Styles compared working on the album to "giving birth ... without the pain".
"It was very exciting. It was nerve wracking."
"But I think honestly any time you are putting something out that's kind of a piece of you, I guess it's quite a vulnerable feeling."