Pam & Tommy actress Lily James told how she was left stunned by Zac Efron's incredible body transformation.
Lily said she even struggled to concentrate on the set of their new film The Iron Claw.
Sixties wrestler Kevin Von Erich is played by 35-year-old Zac in the flick.
Many of his fans were in shock last year after spotting the star backstage looking completely unrecognisable.
Zac, 35, showed off his new look dressed in a knitted grey tank top and skin-tight denim cut-off shorts to reveal his super-tanned, toned legs as he strolled around on the set in Louisiana.
The Greatest Showman star was also sporting a very square-looking pudding bowl-style haircut in the images, leaving him looking a far cry from the clean-cut image fans are more used to.
His transformation was complete with giant muscles, a chiselled six-pack and a bowl haircut for the 2023 film.
Lily, 33, who plays Pam Adkisson, has revealed that her co-star bulked up so much she struggled to concentrate.
She said : “[He had] a great bowl cut, but he was also incredibly muscly which was slightly more distracting."
Lily added: “But what was more incredible is his performance, he has really transformed.”
The Iron Claw focuses on the Von Erich family who were wrestling icons in their 1960s heyday - but went on to be tormented by tragedy after tragedy.
Zac plays Kevin Von Erich - who regularly appeared at his father Fritz's World Class Championship Wrestling promotion.
The sportsman is now 65 years old and was a one-time world champion, having won the WCWA World Heavyweight Championship.
He previously gave his seal of approval for Zac being cast to tell his story despite having never met or spoken to the actor.
