A man in a hoodie who alarmed cinema security turned out to be Hollywood actor Jude Law.
Cinema attendant Connor Walter was asked to keep an eye on a man "acting strangely" at Bath's Odeon on Wednesday.
But Mr Walter recognised the hooded man as Law and arranged a photo with him, even placing a hand-written note in the actor's pocket.
He later received an email from Law apologising for running off.
Law is currently thought to be filming JK Rowling's Fantastic Beasts and Where to Find Them 2 in nearby Lacock, Wiltshire.
He plays a young Dumbledore in the sequel.
Mr Walter said the actor had come to the cinema to watch Detroit and was hoping to remain under the radar.
He said: "I was working as the ticket tearer stood at the bottom of the stairs, and my manager told me to keep an eye on a man acting suspiciously with his hood up in the main foyer.
"The man spent a good 10 minutes just standing around on the phone, then he came and bought a ticket from one of my colleagues and my colleague who served him the ticket did not recognise him, nobody did.
"Then he came to the bottom of the stairs and I tore his ticket, I looked at his eyes and recognised him, then he said 'thanks' and I just knew it was him within an instant."
Mr Walter waited for the film to finish before approaching Law and asking him for a photo.
He said he wrote the actor a "kind note praising his work over the years" and slipped it into his back pocket.
Mr Walter then received an email from the star half an hour later, apologising for running off and praising him for also being a "movie madman".
"If I had not been working that night, nobody else would have recognised him as he was very unrecognisable with his black hoodie and beard," he added.