The Australian actor is known for his long-running role as Wolverine / Logan in the Marvel Comics superhero franchise, and most recently reprised his famous role in new movie Logan.

But while Hugh trained hard to play the mutant Wolverine in the flicks, he admits he wasn't in peak physical condition when it came to filming Bryan Singer's X-Men back in 2000.

"In the first one, I thought you could get into shape in three weeks, and I turned up and the director had pushed all the shirt-off scenes to the very end, four months later," he said during an appearance on The Late Show with Stephen Colbert on Thursday night (02Mar17). "If you go back and see that movie, there's some embarrassing shots."

Logan, directed by James Mangold, is intended to be Hugh's final portrayal of the character after having played the role for 17 years. And in a way, the 48-year-old is surprised he managed to keep up his muscles for such a long time, especially with the punishing diet and exercise regime.

"It's about a three month run-up. So you've got to be in pretty good shape but the three months before it is very specific and it finishes with dehydration. You increase your water intake up to 10 litres of water, three gallons a day. Then you stop about 36 hours before your shoot, but because you've drunk so much water you're peeing all the time. But you lose 10 pounds of water weight," he explained.

Though the father-of-two is pleased to be able to indulge in whatever foods he likes since filming wrapped.

"Now I'm eating and loving it. And sometimes wake up at two in the morning just to go and have breakfast cereal, and then go back to bed," he laughed.