Imagine going to the cinema to watch a film, and then the movie's main star showing up to watch it with you?
That's exactly what happened to some lucky cinema-goers in the US over the weekend, finding themselves face-to-face with Brie Larson, the star of Captain Marvel.
She stunned fans who had come out to see the latest blockbuster film in the Marvel franchise, even serving some of them drinks and popcorn while dressed in a Captain Marvel tracksuit.
She told fans: "I just heard I was on the cups of popcorn and I wanted to see for myself."
But she's not the only celeb to surprise their fans. Do you remember when...
Taylor Swift crashed an engagement party
Taylor Swift gave two super-fans the surprise of a lifetime by turning up to their engagement party.
The singer helped Alex Goldschmidt toast to his engagement to his fiancé Ross Girard in Hollywood, Los Angeles.
As well as toasting the happy couple, she serenaded the couple with an acoustic version of her song 'King of My Heart'.
Emma Watson joined a school hockey game
This must have been one magical game of hockey!
Harry Potter star Emma Watson turned up at a school in London to surprise them during the Hockey Women's World Cup in London last summer.
She's not the only Potter character to shock her fans either.
Eddie Redmayne and Jude Law rocked up at Kings Cross Station
As if heading to Platform 9 ¾ for Back to Hogwarts Day wasn't exciting enough, but fans got to see two of the Potterverse's biggest stars attempting to get through the famous portal.
Actors Eddie Redmayne and Jude Law both star in Fantastic Beasts: The Crimes of Grindelwald and stayed to chat and take pictures with fans as they waited to board the Hogwarts Express.
A penguin in a care home
Ok, so these two aren't technically celebrities, but they're probably the coolest visitors ever at this care home in Berkshire.
Ninety-two-year-old Annie was treated to a surprise visit by two special guests - penguins Charlie and Pringle!
The pair spent some time with Annie after she said it was her wish to see the birds up close.