It is undoubtedly Naomi Watts' most emotional big screen project to date.
The Australian actress plays a survivor of the 2004 Indian Ocean tsunami in The Impossible, a film based on the real life story of Spanish doctor Maria Belon.
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Hugging at the Madrid premiere of the film this week, it's clear both ladies have grown close during the shooting of the movie.
"I'm going to cry," said Naomi on the red carpet, when she was asked about the film and Maria.
The Spanish brunette was on holiday with her husband Henri - played by Ewan McGregor in the thriller - and their three sons in Thailand when the tsunami hit on December 26, 2004.
The film recounts the story of how the separated family fought to find each other, aided by the kindness of strangers.
In a pre-recorded interview for Spanish TV, Maria told Naomi how impressed she was with her handling of the role.
"I was there, and I know how it feels," said the mum-of-three, while both their eyes filled up with tears.
"How it feels is exactly how you portrayed it… That's not acting, it's so much more."
A clearly affected Naomi – herself mum to sons Alexander and Samuel – only just managed to whisper "thank you" as she choked back tears.
At the Madrid premiere, the blonde actress said she was full of admiration for the real life protagonist, who was on hand during filming.
"It was fantastic to work with Maria. It affected me, being with her… She helped us so much. And when she wasn't there she wrote very very long letters."
For her part, Maria was delighted with the outcome of the movie.
“I feel so emotional," she said. "The film has been a great adventure. The expereince was tremendous for everyone. We're here to remember those who didn't make it, and I feel so proud. The Impossible is valiant, honest.
The film's Spanish director Juan Antonio Bayona said he had to keep his emotions in check during the project.
"Those who know me, know I'm quite a cry baby," he admitted.
"But during the 25 weeks of filming, I didn't let myself cry once."
Feeling a big responsibility to bring the story to the big screen, he says: "I gritted my teeth and put up with it," during the more difficult moments.