But the star, 33, says he is still fearful of gaining weight during these unprecedented times.
Speaking to The Sun, he admits that he has to maintain extreme discipline to stay in such good shape.
He said: "People see me now and say, ‘He’s naturally fit — it’s genetics’. But I’m absolutely not.
"My mates call me a ‘chubby boy waiting to break out’ because I love my food.
"And, just like anyone else, if I get lazy and stop working out, I soon notice that bit of flab creeping on."
"I love my food"
Despite his fears, he's been putting in plenty of time and effort while on lockdown.
He regularly shares his workouts, many of which don't require a home gym or equipment.
He shared an entire one-hour workout to his 1.7 million Instagram followers.
Armed with just a yoga mat in his garden, he was interrupted by his dog at one point.
But the ex reality star kept his composure and pushed through the tough routine.
Fans flocked to praise him and the quality of the workout.
One user wrote: "Great workout mate. I've been doing all of them!"
"I had a great work out"
And another praised: "Thank you! I had a great work out. I may join in again tomorrow. Is this HIIT training? I really liked the variety of work outs and easy enough to follow at home."
And a third wrote: "Amazing! Thank you so much... we complete your workout every day! They’re absolutely brill."
Meanwhile his wife, actress Michelle Keegan, has opened up on what it's like to self-isolate with Mark.
Speaking via video call to Heart FM hosts Jamie Theakston and Amanda Holden, she joked about their time together.
She said: "I feel like it's been six months already, Jamie!"
The Our Girl star added: "One day I’m fed up, I have a tantrum about it and I miss my family, but then on another day I think, 'you know what, we’re actually in a good position', we’re at home'."
The couple currently live together in their lavish mansion in Essex.
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