Simon Cowell jokes he will release a fitness DVD with David Walliams.

The 'Britain's Got Talent' boss has stunned fans after dropping 20lbs - which he has credited to a new vegan diet on the expert advice of a doctor in Los Angeles - and he teased the possibility of teaming up with his fellow judge to share his secrets.

Appearing on ITV's 'Lorraine' this week, David - who says he's also ''lost a tiny bit of weight'' - cheekily quipped: ''Are you doing a workout video?''

Simon laughed: ''I could do one with you, yeah.''

Their comments come after the 59-year-old media mogul was forced to deny claims he had a gastric band fitted to help with the weight loss.

He recently said: ''People have said: 'Oh, he's had a gastric band fitted' - but I haven't. If I had, I would admit to it. This diet is all about what you put into your body.''

Instead, Simon listened to an expert as a doctor sought to change his ''appalling'' diet.

He explained: ''I met this doctor in LA and he told me my diet was appalling and I had to cut out fatty foods and certain drinks.

''I could see the difference. Cutting out sugar made a massive difference. The first few weeks were difficult, but then I actually stopped craving sugar.

''I had also found a brilliant gluten-free beer, which helps.''

The talent show judge admitted the most difficult part of his lifestyle changes come from watching his five-year-old son Eric snacking on tasty treats he's decided to cut out.

He said: ''The hardest part is when I see Eric eat pizza in front of me. That's really tough.''

Simon had previously ditched junk food and adopted a vegan diet following a health scare almost two years ago when he fell down the stairs at home in the middle of the night.

He said at the time: ''I cut out a lot of the stuff I shouldn't have been eating and that was primarily meat, dairy, wheat, sugar -- those were the four main things.''