The big question hanging over Christopher Nolan's forthcoming war movie Dunkirk is not simply whether it's any good or not or how it ends (check Wikipedia, kids!) but what the hell Harry Styles is doing there.
No offence to the singer, but he's never acted before (unless you count pretending not to be terrified of One Direction fans) and he's part of an ensemble that includes some of the finest onscreen talents alive today - Tom Hardy, Mark Rylance and Cillian Murphy to name just three.
So what was behind Nolan's decision to cast him? Surely not just a cynical attempt to drum up publicity and put (teenager, terrifying) bums on seats?
It's a question the director had been facing head on since promotion for the film began, and it's fair to say Nolan has came out swinging for his young star.
In an interview with Entertainment Weekly, he defended casting Styles and even compared it to giving Heath Ledger the part of The Joker in The Dark Knight.
"As a director, I have to trust my instincts, my ability to figure out who's the right guy for the part. I'm not too worried about baggage," Nolan said.
"I was new to Harry. I mean, I've heard his name from my kids, but I wasn't really familiar with him… What I was seeing [when he auditioned] was a very charismatic guy who clearly had a truthfulness and a subtlety in his ability to perform as a film actor.
"When I cast Heath Ledger as the Joker [in The Dark Knight], 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."
A surprising comparison, perhaps, given that Ledger was well established as an actor at the time – and that he notoriously threw himself method-style into that role on and off set. Does that mean the young Styles went around for months pretending to be a young soldier from 1940?
"Harry was very committed and determined to just being one of the guys and coming there and learning what he could from the most experienced people around him and diving into the role feet first," Nolan continued.
"I think he's done an incredible job on the film and I'm really excited to show it to people."
A successful transition from pop star to actor is, of course, not without precedent - just as Justin Timberlake - and it sounds like Harry went about it the right way, so good luck to him.