WATCH: Billy Graham's grandson tells what it was like playing his grandfather in 'Unbroken' sequel

Will Graham is not an actor. He's a preacher. He wants to make that perfectly clear to anyone who sees his role in "Unbroken: Path to Redemption."

"It gave me an ulcer," Graham said with a laugh, talking about the experience of being in a movie.

Graham is portraying his grandfather, the late evangelist Billy Graham, preaching at the famous Los Angeles Crusade in 1949 — a series of sermons that changed both Billy's and movie protagonist Louis Zamperini's lives forever.

Zamperini, the war hero and Olympic champion who survived detainment in a Japanese prison camp (portrayed in the movie "Unbroken"), developed a life-changing bond with Billy Graham when he returned to the U.S. after first hearing the evangelist preach at those Los Angeles tent revivals.

Even though Graham was playing the role of his grandfather, he was not trying to act like him exactly.

"I looked at my granddad's sermons, how he preached," Graham said. "I didn't try to emulate him. Matter of fact, the director told me not to emulate him, but just to be yourself and you'll come off more natural, because I was real nervous. I'm not an actor."

As a result, Graham was preaching his grandfather's sermons word-for-word in the movie, but in his own unique preaching style. And as far as he's concerned, that's where his movie career will end.

"Great experience, but I don't want to be an actor," Graham laughed. "I peaked, and I want to retire at my peak."

"Unbroken: Path to Redemption" premiers nationwide on Friday.