Joe Wicks, the famously curly-haired personal trainer, is best known as ‘The Body Coach’ to his fitness disciples.

Three years ago, Joe launched his subscription-based 90 Day Shift, Shape and Sustain Plan, and went – stratospherically – from sharing amateur recipe videos and free fitness workouts online, to helping thousands of people trim down and get fit for a living.

Now the Epsom-born fitness coach has a not-too-shabby 1.8m Instagram followers and 274k on Twitter, and he’s launched his fourth cookbook, Cooking For Family And Friends.

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Brimming with openness and charm, you can see his appeal – a combination of endless enthusiasm that pours out of him with every flick of hair or inadvertent muscle flex, and a monumental work ethic.

That and the fact he’s not in the least bit starry, as he sits on a London rooftop terrace awaiting a ‘Joe-mito’ (a riff on his watermelon and mint ‘posh slush puppy’), at the launch party the new cookbook.

He even excitedly, and non-ironically, Snapchats a selfie from in front of a bigger-than-life-sized poster of himself. Best to get it out of the way early in the night too – after all, he’s built his career through social media, but he still has rules: “I never do social media when I’m drunk, because I might think I’m being really funny, but am really saying the worst thing ever!”

Cooking For Family And Friends marks the halfway point in an eight-book deal for Joe, and is a more inclusive follow-up to his wildly successful trio of Lean In 15 cookbooks (all three still grace the bestseller charts, and sales have topped 2.4 million).

This time around, he’s catering for busy dinner tables, rather than just solo gym bunnies.

“You know how sometimes you feel like, if you’re on a diet, it’s just you on your own? I wanted you to think, well actually, you can have barbecues and parties and make them healthy,” he explains. “You can still batch cook and make your kids’ lunch.

“In fact, the whole family won’t even know it, but they’re eating healthier, so are going to get leaner, without anyone saying, ‘You’ve got to eat this, you’ve got to eat that’.”

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The former boot camp trainer has, perhaps surprisingly, included a few treats too – namely his all-time “top desserts”, sticky toffee pudding and chocolate fondant. “Just because chocolate isn’t ‘clean’,” he says, fingers miming air quotes, “doesn’t mean you can’t enjoy it and have it now and again.

“I’m not like, ‘Don’t eat this’, and, ‘Clean eating that’. Just enjoy your food! If you exercise, it works out, you know?” he says, adding with a cheeky-chappy grin firmly in place: “This is how I roll.”

Joe admits that no one person got him into cooking – “it was just myself really. My mum couldn’t cook very well,” – but in terms of becoming an entrepreneur, his ultimate hero is, without doubt, Jamie Oliver. Without taking a breath, he reels off his every encounter with the Naked Chef, the most recent being when the duo grabbed dinner together at Jamie’s restaurant Fifteen.

“We sat there for four hours on our own, talking. He’s just so generous with advice, he downloaded all this wisdom and knowledge and experience.

“He’s on a mission. I told him, ‘Mate, you work hard’,” says Joe, visibly galvanised.

And, aside from writing another four books, what else is left on his own mission?

“The message is, no matter how old you are, you can exercise and feel good; you can take control of your body, you don’t have to starve yourself.

“I’m for everyone; fitness and food for everyone.”