The TV personality posted a photo from his Christmas celebrations on Twitter where he looked almost unrecognisable as he held a Pointless board game.
"This was my secret Santa at the Northwich Panto. I suspect Richard Osman," he captioned the snap.
However, people were less interested in his Christmas gift and more stunned by his new look.
"That's an amazing achievement. Well done Mark. Hope you're well," one fan said.
"Is it bad I thought this was a throwback pic of you as a teen!? You're looking way younger, Beastie!!!" another wrote.
"Looking great you should be proud of the work you’ve done. I know it wasn’t easy," a third added.
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"Almost didn't recognise you, really smashed that weight loss," a comment read.
Some however shared their concern after the 57-year-old's dramatic weight loss.
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"You look unwell and have gone too far with the weight loss, look after yourself Beasty Boy," a fan said.
"Looking good, Mark.....but enough is enough now. Some folk get a tad obsessed when losing lots of weight. You look great," another commented.
"Mark I get being in shape was needed but ... you kinda need to bring some weight back. Not all just some."
Mark, who tipped the scale at 184kg before his weight loss, told ITV's This Morning he lost weight by cutting carbs and sugar from his diet.
He added he did not have any surgery to help with his weight loss and doctors had told him a gastric band procedure could be dangerous due to how his body digests sugar.
The star, who was diagnosed with type 2 diabetes in 2017, told talk show Loose Women he was also on the verge of getting pills for high blood pressure.
"I'm eating an awful lot of lean meat and as much as I love chips and other carbs I'm having quite a bit less than I used to and its sort of become a virtuous cycle – I'm not feeling that hungry so you're eating less so you lose weight," he said.