Mark Wahlberg reveals astonishing body transformation: 'This is 50'

Mark Wahlberg has shown off his impressive physique in a new Instagram video, and fans can't believe he's looking so ripped at 50-years-old.

Flexing his biceps and abs in a bathroom mirror, Wahlberg spoke to the camera, "This is 50," he said, before plugging protein brand Performance Inspired Nutrition, who he's partnered with.

Watch the video above.

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Fans have shared their amazement at Wahlberg's physique, with one writing: "No way you're 50 dude!! 👏"

Another commented: "Killin it my man!"

Wahlberg has bounced right back after he revealed he gained more than 13kg for his role in the upcoming film Father Stu, where he played a boxer-turned-priest.

Speaking with KIIS FM's Kyle and Jackie O on their radio show, the 50-year-old recently called the process of gaining weight "difficult", particularly now he's older.

"I put on 30 pounds (13.7kg)… that was really difficult. I'm not getting younger," he told the radio hosts, adding "I would say it's easier to stay in shape than it is to get in shape."

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Wahlberg first revealed he had gained weight for the film during an appearance on The Tonight Show Starring Jimmy Fallon.

"Unfortunately, I had to consume, for two weeks, 7000 calories, and then for another two weeks, 11,000 calories [a day]," Wahlberg said — 11,000 calories is the equivalent to almost 20 Big Mac burgers from McDonald's. "It was fun for about an hour."

He added: "It's such a hard, physical thing to do. Losing weight, you just kind of tough it out, you just don't eat, and exercise."

Last year the actor revealed he gained 9kg in just three weeks while on his weight gain journey.