"He really motivated me to get in shape for this movie," Zac told Entertainment Tonight about the iconic athlete while attending the Nov. 8 premiere in Dallas. "The physicality he brought to the ring every single day was really unique. It changed wrestling. I knew that was going to be the hardest [thing] for me to master and get right."
But he rose to the challenge, noting, "I put everything I had into it."
For one, Zac and his costars—which includes Harris Dickinson and Jeremy Allen White—had to rock very '80s hairdos. And for Zac, that meant a shaggy bowl cut—which is no small feat!
"I remember Harris and I were walking out of hair and makeup," Zac recalled to ET, "and it was the first time we had to wear the full kit, and we were both thinking, 'What the hell are we doing here, man? How did we get into this?'"
As he put it, "It was shocking at every point of the transformation."
Despite sporting the 1980s hairstyle, Zac praised the studio's glam team their all-star skills. "I think it ended up looking really good and we had a great crew helping us out with that," the actor added. "The hair and make-up team was epic."
That appears to be the sentiment all-around, as the former Disney Channel star revealed the winning compliment he received from Kevin, the legend he played on the big screen.
"He told me he was happy with it last night, so I'm stoked!" Zac gushed. "I cried a little bit, if I'm going to be completely honest."
The 36-year-old's trainer Chavo Guerrero Jr., who is also a pro wrestler, also shared the love.
"He's a machine," the fitness expert exclusively told E! News on the red carpet about Zac. "In-between training, he was like, 'I gotta get a meal in or I gotta get this protein shake in.' He was just on top of it constantly. And really, you know, abs are made in the kitchen, not in the gym."
Keep reading to see Zac's buff new body before The Iron Claw hits theaters Dec. 22.