The Little Mermaid 's Jonah Hauer-King got too buff while training to play Prince Eric

Jonah Hauer-King made the wrong kind of splash when he bulked up like a Marvel star to play Prince Eric in Rob Marshall's new live-action take on The Little Mermaid.

For his role as the young seafaring prince, to actor had to get in shape. But when the coronavirus pandemic halted production on the movie, he ended up with eight extra months to prep and got a bit too buff, his trainer Sana Shirvani told Insider in a recent interview.

Shirvani had put Hauer-King on a traditional bodybuilding program designed to give him lean muscle without gaining fat. "It was a standard bodybuilding program, so we would do, for example, back and biceps, chest and triceps," she explained. "We would focus solely on getting a little bit of strength, a little bit of size into his body."

Disney; Andrew Toth/Getty Images Prince Eric in Disney's animated 'The Little Mermaid'; Jonah Hauer-King from the live-action remake

A little, however, became a lot.

"We got him to that point, and then obviously if he continued training in that capacity, he was only going to get bigger and bigger," Shirvani said. "I remember the director coming up to me and saying, 'We are not after the Incredible Hulk, we want a strong sailor boy.'"

As a result of his unintentional new superhero physique, Shirvani put Hauer-King on a calorie surplus with loads of protein and reduced his training. "He was so, so dedicated," Shirvani said. "His professionalism was so good that he just said yes to everything I threw his way."

In EW's Around the Table with the Little Mermaid cast and crew, producer John DeLuca and Co. called the remake — which features acting in the water and its stars donning harnesses to emulate swimming scenes — "truly the most technically difficult thing we've ever faced."

Photo courtesy of Disney Jonah Hauer-King as Prince Eric and Halle Bailey as Ariel in 'The Little Mermaid'

Marshall told the cast, which includes lead Halle Bailey (Ariel), Melissa McCarthy (Ursula), Javier Bardem (King Triton), Daveed Diggs (Sebastian), Awkwafina (Scuttle), and Jacob Tremblay (Flounder), "You were all fearless too, and that was the thing. John and I kept saying from the very beginning, 'We cannot let the technical end of this lead it.' It can't be about the teeter-totters and the tuning forks and the wires. It has to be about story, it has to be about character, it has to be about feeling, and that's what you brought."

The Little Mermaid is in theaters now.

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