Matthew McConaughey has revealed how he ended up acting with two generations of his family in The Lost Bus, a film about trying to escape California’s deadly 2018 wildfires.

The Oscar-winning actor plays Kevin McKay, a school bus driver navigating 22 schoolchildren and their teacher through a raging inferno to safety.

But behind the scenes, the film was a family affair for McConaughey.

Kevin’s mother and son were portrayed by the actor’s own 93-year-old mum, Mary Kathlene ‘Kay’ McConaughey, and 17-year-old son Levi, in his first screen role.

“Just to be in a scene with those two, I never thought that was something that would happen,” the star says.

The film is a real-life depiction of the devastation caused after a power line fell, releasing sparks onto the tinder-dry Sierra foothills.

The resulting wildfires burned for 17 days, killing 85 people and displacing more than 50,000, destroying most of the town of Paradise and much of the nearby communities.

In what Vulture has called “an instant disaster-movie classic”, McConaughey stars opposite Barbie’s America Ferrera, who plays teacher Mary Ludwig.

Mary and Kevin have to make split-second decisions that could save or kill everyone on the bus, all while worrying about the safety of their own families.

Kevin already has a lot on his plate – his father has died, his mum is unwell, his marriage has broken down and his teenage son wants to move back with his mother.

This is before he discovers he’s the only driver who can help Mary and the children.

McConaughey says the decision about casting was down to director Paul Greengrass.

“Paul Greengrass started as a documentary film-maker, so his interest in truth, in reality, is very important,” the actor says.

Greengrass is arguably most famous for the Bourne action-thriller films starring Matt Damon. His other movies include real-life dramas Captain Phillips and United 93, the latter of which earned him a 2007 Oscar nomination.

He’s known for using non-actors to play themselves, so using members of McConaughey’s family is part of this realism.

Levi got the role after persistently asking his father to be considered for it.

“I always pitch the script to my family, whatever film I’m doing,” says McConaughey.

“I tell the story, and that this character I’m playing has a son. My son Levi comes to me and he says, ‘Can I read for it?’

“I went, ‘Huh’. Didn’t say anything,” McConaughey recalls with a smile.

“I wanted to see how much he wanted it.”

After Levi asked four times over several days, McConaughey conceded he could submit an audition film – but insisted his last name was removed.

When Greengrass saw the video, he immediately said, “This is the kid” – before discovering who Levi was.

Kay was cast later on, after Greengrass asked McConaughey if his mother would audition.

“I was like, ‘Trust me, she’s a performer, but she actually just fell and broke her tailbone… and she’s in a wheelchair’,” the actor says.

That wasn’t a problem for Greengrass, who cast Kay after seeing her audition video.

Greengrass’s focus on reality meant he also ditched his initial plan to use a virtual set around the bus to make the film.

“I got cold feet,” he tells the BBC. “I felt it wasn’t really me as a film-maker to be so virtual. I wanted to be out in a real world.

“So in the end, we got an abandoned campus in New Mexico, a huge area with many roads, and we decided to do it for real.

“We built everything and had all the real vehicles, and were able to lay gas lines. We couldn’t burn anything that created particles in the air, for obvious reasons, because you might start a forest fire. But with gas burning, it’s safe.”

The wildfire is so dominant it’s arguably the main character in the film – the footage was either real, created by the gas lines, or by visual effects augmentation, using shots of real fires.

“My aim was to try and make the most realistic cinematic experience of fire,” Greengrass adds.

He can of course see how pertinent this is – there have been recent wildfires around the world, including in California in August.

“Wherever you look you see these enormous wildfires – the world is on fire – it’s part of the global dangers we face.

“What I loved about this film was it had those simple elements of the human story, and yet it spoke to something universal.

“All the intersecting storylines in that film are about characters grappling with the idea of having left it too late.

“That’s the story of our world today, I think.”

One of the film’s producers, Oscar-winning actress Jamie Lee Curtis, came up with the film after reading a Washington Post article about Lizzie Johnson’s book Paradise: One Town’s Struggle to Survive an American Wildfire.

It included a section about Kevin McKay and Mary Ludwig.

“I remember I looked at my husband and I said, ‘Well, that’s the movie’,” she says.

Curtis called up fellow film producer Jason Blum with her idea.

“I think it’ll be the most important thing either one of us does as film-makers in our in our lives,” she told him.

Greengrass then came on board, and says he’s especially “drawn to people in the real world, placed in extraordinary situations”.

“That always interests me, because I think you see more of what makes us human.”

He felt “lucky” to get McConaughey and Ferrera because “they sit in that kind of real-world register I like to put my films in”.

Curtis also reveals how the film has brought her new, close friendships with the real Kevin and Mary.

Kevin told the actress his last happy memory with his mother, who has since died, was when they saw the 2018 movie Halloween together – which of course starred Curtis.

Meanwhile, the real Mary told Curtis they shared a “weird connection” – Mary’s father dated her mother, actress Janet Leigh, before she was famous.

”Mary told me, ‘I only saw my father cry twice – the day my mother died, and the day your mother died’,” Curtis says.

“So in a weird way, this has come full circle.”

McConaughey praises the real-life pair’s “sacrifice”, saying they represent all the first responders during the wildfires.

“The truth is, every person in Paradise is a hero,” he adds.

The Lost Bus is out in cinemas now and will be in available on Apple TV+ on 3 October.