Jessica Biel and Justin Timberlake's son Silas makes cameo in Matchbox: The Movie

Jessica Biel and Justin Timberlake's eldest son makes a small cameo at the end of Matchbox: The Movie.

The 44-year-old actress and 49-year-old former professional wrestler John Cena star in the Apple TV film, which follows the latter's character, spy-and-former soldier Sean Walker, and his childhood pals as they try to find a nuclear warhead and clear their names after being blamed for the theft.

Speaking about Silas, 11, Jessica told E! News: "He plays a small part in this in the movie at the very end, which is really cute."

Silas, and his brother Phineas, six, who are huge fans of John, joined Jessica on set, and they were amazed by the experience.

She said: "They're so funny. I feel like their brains implode whenever they come to set - especially a set like this where there's a hero of theirs that they're meeting, there's cool action sequences, there's fight sequences."

However, Phineas got confused while on set about what was acting and what was not.

Jessica said: "My little one, I think he was like, 'Is this real? Is this not real?' John just got punched, and he fell on the ground.

"I don't even know what is happening to their brains or what they're thinking. It's just a lot of confusion."

She added: "My 11-year-old is like, 'I know what this is.'

"But the six-year-old is still like, 'What's happening here?'"