Lord of the Rings star Viggo Mortensen has recalled a terrifying experience while filming underwater for his new movie Thirteen Lives.

The film tells the miraculous true story of the Thai cave rescue in 2018, where a football team was saved by a group of divers. Mortensen takes on the role of diver Rick Stanton, appearing alongside Colin Farrell as John Volanthen and Joel Edgerton as Richard Harris.

Speaking about working with his real-life counterpart, Mortensen explained during a recent press conference: "In this case, it was crucial, especially for what we had to do underwater.

viggo mortensen, colin farrell, thirteen lives
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"Rick Stanton was there during rehearsals where all the actors, Jason Mallinson came also, and they helped us to not only swim like them and move like them, but also to be safe. The way we worked as a team reflected what they described to us, what the rescue entailed," he continued.

"We were really worked together above water as much as under water. Underwater, I would say was maybe even more important because even though you're shooting a movie and it's somewhat controlled situation, whenever you're underwater and you're in caves, it's dangerous.

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"I think all the actors, we listened very carefully to what they were telling us and watched what they did very carefully," he added.

"Everybody worked hard, everybody pulled together. It reflected the real rescue and it was a very selfless team-oriented effort shooting the movie as well. It felt, at times, very real. Sometimes too real, there were some very tight spots underwater."

Recalling one important piece of guidance, the star continued: "One thing Rick kept talking about was, 'Remember to just breathe calmly. Control your breathing'. The more nervous you are and you're breathing shallow, you're using up all your air.

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Related: First trailer for Star Wars and The Batman stars' new movie Thirteen Lives

"There were a lot of places that were so narrow that you had to just wiggle through. Sometimes you had to take your tank off, while you were underwater, without disconnecting from the air, then go through this area [and] put the tank on," he continued.

"Do this all calmly. We had two tanks. If something went wrong with one, just be calm. Don't freak out, because you can drown in a few seconds. Once you freak out and you swallow a little water, you're done. Even though it's a movie, nobody can get to you fast enough."

viggo mortensen, colin farrell, thirteen lives
Prime Video

However, things turned pretty terrifying for him at one point, Mortensen revealing that he rolled on one of his tanks while attempting to squeeze through a tight spot, which resulted in it stopping working.

"I was like, ‘F**k, no air'. It seemed like it took forever [to swap to the other tank]. It probably didn't take that long, but I got it done, and then I managed to get through this tight spot," the actor recalled.

"But I really had a moment there where I started to breathe fast. It's very dark. You can easily get very frightened in a hurry. Like I said, breathing, breathing. That was the key."

Thirteen Lives will be released in select cinemas on July 29 and on Prime Video on August 5.

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Sam is a freelance reporter and sub-editor who has a particular interest in movies, TV and music. After completing a journalism Masters at City University, London, Sam joined Digital Spy as a reporter, and has also freelanced for publications such as NME and Screen International.  Sam, who also has a degree in Film, can wax lyrical about everything from Lord of the Rings to Love Is Blind, and is equally in his element crossing every 't' and dotting every 'i' as a sub-editor.

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Movies Editor, Digital Spy  Ian has more than 10 years of movies journalism experience as a writer and editor.  Starting out as an intern at trade bible Screen International, he was promoted to report and analyse UK box-office results, as well as carving his own niche with horror movies, attending genre festivals around the world.   After moving to Digital Spy, initially as a TV writer, he was nominated for New Digital Talent of the Year at the PPA Digital Awards. He became Movies Editor in 2019, in which role he has interviewed 100s of stars, including Chris Hemsworth, Florence Pugh, Keanu Reeves, Idris Elba and Olivia Colman, become a human encyclopedia for Marvel and appeared as an expert guest on BBC News and on-stage at MCM Comic-Con. Where he can, he continues to push his horror agenda – whether his editor likes it or not.