Godzilla: King of the Monsters director Michael Dougherty has told RTÉ Entertainment that the film's star Millie Bobby Brown is "an old soul".
The actress, best known for her role as Eleven in the Duffer brothers' hit Netflix show Stranger Things, makes her film debut in the blockbuster movie, which was directed and co-written by Dougherty.
The American filmmaker said she is "phenomenal" in the role.
Speaking to RTÉ Entertainment, Dougherty said of the British actress, "She's an old soul. She might be 15-years-old but there's an old soul in there and it really came through in her performance.
"But at the same time, as soon as you call 'cut', she's just a girl again, really bubbly and fun. We had a really good time on set, whether we were pranking each other or the other cast members."
The star-studded sequel to 2014's Godzilla features a wealth of acting talent, including Friday Night Lights legend Kyle Chandler; The Conjuring star Vera Farmiga, and The West Wing's Bradley Whitford.
Dougherty said he had "a lot of fun" working with them.
"I love working with actors that I'm a fan of. It's intimidating, but you tend to learn a lot from them, they come with such a wealth of experience. It makes your job a lot easier hiring great actors because you just have to turn the camera on and they do their thing," he said.
The director shed some light on how he got the best reactions out of the cast, who had to film a lot of scenes involving the epic monsters in front of a tennis ball.
Dougherty said: "I had some tricks! I loved bringing the actors in to look at the concept art, and the creature maquettes, the little statues that we made. We did pre-viz animation, which is rough, 3D animated versions of sequences, so the actors had a sense of what it was that they had to imagine when they were looking at the green screen or tennis ball.
"But then on set I would also play the roars of the monsters, and that really helped sharpen the performances, to hear the screeches and the growls. It made their eyes go a little bit wider, got their heart racing and just made their reactions a little bit sharper."
The director grew up watching Godzilla movies and says directing this film "feels like a birthday wish that finally came true".
He hopes this film will introduce the world of Godzilla to a whole new generation.
"Honestly, the idea that this is the first Godzilla film that younger kids will see [that] really is the hope," he said.
"That this will inspire the next generation of Godzilla fans and maybe the next possible Godzilla filmmaker. That's how I got started, that's how I got inspired was watching the original films from the '60s and '70s, so who's to say?"
Godzilla: King of the Monsters is out in cinemas now.