The 54-year-old went shirtless for the selfie as he showed off the results of his new fitness regime.
Gregg has lost four stone since taking on a personal trainer and changed his eating habits, with the presenter now weighing just under 13 stone.
As well as regularly hitting the gym with his PT, Danny Rai, to work out, Gregg has also made big changes to his diet, revealing that for the last two years he has cut back on fatty foods and booze and chooses lean meats.
“I made a conscious decision to cut down on fried and high sugar foods, as well as booze — which helped me lose weight,” he said in 2017.
“When I was at my biggest I was having a daily fry up, fish and chips once per week, takeaway a couple more times and drinking beer nearly every day. At first, I felt like I was missing out.
“But my body got used to what I was giving it and yours will too.”
A painful stomach condition also means the star has to steer clear of certain foods.
Gregg was diagnosed with diverticulitis last year, but has been encountering problems because he often “forgets” to stay away from food that makes it worse.
Diverticulitis sees parts of the large intestine (the diverticula) become inflamed, which leads to severe pain and other symptoms, including a fever.
Gregg’s diagnosis came when the inflammation he was suffering left him “almost doubled up in pain”.
“At that point they can burst your intestine,” he told the Mirror.
“When they’re irritated, you’ve got to watch alcohol and spicy food,” Gregg continued. “We were eating chilis yesterday. Before that I had a massive skinful of beer in Dublin and it was already playing up.
“I forgot, because I’d been so well. But yesterday I was ill. I’m turning into one of those old people who has things wrong with them.”