Austin Butler drank microwaved ice-cream to gain weight for his award-winning portrayal of Elvis Presley.
The Elvis star, 31, who secured a Golden Globe award for his role as the music icon, followed Hollywood star Ryan Gosling's method for weight gain, and would eat doughnuts by the dozen.
However, the experience left him feeling "awful", he admitted.
Austin's dedication to his breakout role has been well documented, with the star admitting he "lost touch" with who he is, and his vocal chords were damaged.
He also didn't see his family for three years as he prepped for the movie, and then filmed the biopic, which charted Elvis' rise and tragic death, in Australia.
Speaking to Variety about his weight gaining method, Austin said he copied Ryan Gosling, adding: "I heard that when he was going to do The Lovely Bones, had microwaved Haagen-Dazs and would drink it.
"So I started doing that. I would go get two dozen doughnuts and eat them all. I really started to pack on some pounds."
"It's fun for a week or, and then you feel awful about yourself, so I did that for a while," he said.
He added that at first the film was going to be shot chronologically, but because of COVID, that had to change.
"One day we'd be in 1974 and the next day we'd be in 1956. So you got to be able to switch back and forth, vocally and physically," Austin explained.
The Carrie Diaries star surprised fans last month at the Golden Globes, as he accepted his award with an Elvis-style twang.
The actor later admitted he is trying to get rid of the Tennessee accent and said his vocal chords took a hit "with all that singing".
"I am getting rid of the accent, but I have probably damaged my vocal cords with all that singing.
"One song took 40 takes," Austin said while appearing on The Graham Norton Show.
Austin's voice coach Irene Bartlett recently spoke out about his Elvis accent and said it's possible it will remain "forever".
"What you saw in that Golden Globes speech, that's him. It's genuine, it's not put on," she said during an appearance on ABC's Gold Coast.
Austin has also been candid about the personal toll the role took on him.
"During Elvis, I didn't see my family for about three years. I was off in New York prepping with Baz and then I went to Australia.
"I had months where I wouldn't talk to anybody - and when I did, the only thing I was ever thinking about was Elvis," Austin said in an interview with Variety.
The star has said that he loved every minute of filming, but said there were some negative aspects of the role and explained how he ended up "not knowing" who he was by the time filming wrapped up.
