Pulling up his shorts to reveal his noticeably slender legs, the 43-year-old appeared miles away from his usual, muscly self.
The star’s weight-loss came down to what he called “starvation” after spending a stint on the brutal island.
Iwan recently came under fire after killing a caiman alligator as the islanders went to extreme lengths for food.
He told the GMB team: “It was a do or die situation. It sounds cruel, but I felt no remorse when I killed that caiman.
“I know that’s horrible. There was no pleasure in killing it, but we were starving.
“I feel bad that we took an animal’s life, but we had to eat,” the Welsh sprinter added.
He appeared with his co-star, Shazia Mirza, who despite being a vegetarian, agreed that they had to kill the reptile.
The 43-year-old explained: “Listen, I’m a vegetarian and I hadn’t eaten meat for eight years. But at that point on the island, we hadn’t eaten food for nine days.
“We had no food at all. I know people watching at home probably think producers were secretly bringing us packets of crisps or pieces of cake – well, they weren’t.
“Whether you’re vegan or vegetarian, if you’re in a life or death situation, you will do anything to survive,” she explained.
The comedian found herself in a dramatic situation on last night’s instalment of the survival show after she slipped on wet rocks knocking her unconscious.
Thankfully, she was allowed to return to camp after being observed by Bear Grylls’ medical team was described as: “Bumped, bruised, but [an] absolute trooper!”