The actor said that the image, which was widely speculated to have been heavily photoshopped, was the result of a gruelling exercise regime.
"That's all me, man," Jackman said on The Jeff Probst Show, adding that he was annoyed that people thought it was a fake.
"Because it was brutal getting there. And by the way, I asked the company if they could just... you're spending millions on special effects, just help me out. I want to eat pizza and drink beer. And they said no.
"For that kind of body, I had to go up in weight, big, lift big and heavy, then strip down."
Jackman has teased that one of his fellow X-Men stars will join him for a cameo in the upcoming movie. He will also appear as Wolverine in X-Men: Days of Future Past.
The Wolverine, which is directed by James Mangold, will arrive in cinemas on July 26, 2013.
Watch the full interview with Hugh Jackman below: