She didn't tell him. Not then or in any of their phone calls during his time in Jindabyne filming the show.

"I just couldn't, he'd trained so hard," she said. "He would have cancelled for sure - and if he didn't, it would have been on his mind the entire time."

Ponton didn't find out until he returned two weeks later. (He is now OK, but has to be monitored.)

"The two words in life you never want to hear: 'son' and 'tumour'," he says now.

"I would have turned around and come home straight away. It took amazing strength for her not to tell me.

"She didn't let on that anything was even slightly wrong. I didn't know she had that strength, it just blew me away. It's so comforting knowing that behind the scenes the fires are burning bright."

The show was so hard, he says, physically and mentally, that any niggling anxieties would have affected the performance of contestants.

As it is, when we meet three weeks after the show has wrapped, he still has trouble getting warm.

At 46, the father of three (besides Bronx, there's son Max, eight, and daughter Milla, six) was one of the elders of the show, and by all accounts he did pretty well.

But he's used to working hard. By the time I meet him at 1pm on a Friday afternoon, he has appeared on Sunrise and led a Basic Training class, a Spin class and a couple of personal training sessions.

After our chat, he's hoping to squeeze in a surf with Max and host more sessions before the sun sets. He says he's always the one at the park climbing the jungle gym or playing touch with the kids.

"I never waste a moment," he says, as we walk the beach near his North Curl Curl home. "What's the point of standing on the sidelines with your iPhone talking to your virtual friends? So many adults tell their kids to get out there but they don't do anything themselves. I'm determined to fit as much as I can into every day. If that moment in time passes, I'll never get it back."

Ever since he could walk, Ponton dreamed of playing professional rugby league. He was contracted to Norths at the age of 16, until debilitating knee and shoulder injuries steered him into coaching.

He worked as strength conditioning coach for five years for the Bears, before going into gyms and becoming a leading trainer and competitor across multiple disciplines, including aerobics, Spin, Step, boxing and Pump.

"I was told I couldn't play football ever again and at the time I thought that was the greatest travesty in the whole world." he says. "But I've made a much better career as a trainer than I ever would have as a rugby league player who was probably always going to be a little bit small anyway."

The Biggest Loser called in 2007 and took over his life for the next 10 years. He took a break from television, before returning to show off his many tattoos in last month's strip tease reality show The All New Monty and then signing up for SAS Australia - the hardest thing, he says, he's ever done.

"The SAS nearly broke me," he says.

"It was next level. If you can imagine all of your worst nightmares rolled into 14 days, that's what the SAS selection process is. There's claustrophobia, there's hot, there's cold, there's no sleep, there's no food.

"There's never enough time to get ready, enough clothes to stay warm, enough food to fill your belly, time to pack your bag. If you're at the back of the march, you've got to be in the middle of the march, if you're in the middle you need to be at the front, if you're at the front you have to be further in front.

"Nothing is ever right. It's basically deprivation of all your liberties and then see how you cope and react under pressure. It has scarred me."

As a fitness trainer, he knew he would be under extra scrutiny, so he trained hard in the lead-up, including with Bondi Rescue's Dean Gladstone, who taught him how to do the Wim Hof method - a combination of meditation, breathing exercises and exposure to cold - to help control his endurance and state of mind.

"I'm a firm believer that you can train yourself to do anything," he says, adding that he's now thinking about training for a professional boxing bout. "I'm that guy that always needs a challenge. I can't relax for 10 minutes."

Last July marked 30 years as a registered trainer. "There's not many of us that have done that long," he says. "Every day I wake up and I go: 'Can you believe I actually get paid to do this?! This is incredible!' I'm so thankful and so happy."

He believes the reason he is still successful, and loving what he does, is because he has never strayed too far out of his lane. To him, the TV roles are just an extension of his training, although instead of reaching a few people in a class, he can reach a million.

"I've found my calling and I've never stepped outside my bounds - by opening a gym or starting a franchise or whatever," he says. "I think that's where a lot of people go wrong. I'm lucky I'm a very good trainer. I'm probably a s**t businessman and I'd probably be very bad at running a new gym! It's better to stay doing what I know and love rather than trying to big-note myself and step out."

It's a formula that seems to be working, and his bouncy exuberance is infectious.

"You can't fake my enthusiasm for life, it's impossible!" he laughs. "I really actually am like that all the time. I'm a mad frother. It doesn't matter if I'm pushing my son on a wave or teaching a class, I honestly believe that to be doing what I'm doing every day, I'm blessed."

Despite constant event invites, he says he shuns the red carpet for nights at home, or surfing with the kids, coaching Max's Harbord Devils footy team and trying to master the North Curly skate park.

"I love being a dad, it's the best thing ever," he says. "Kids are amazing. One of my primary motivators to stay fit and healthy is to be able to do all the things I want to do with my kids."

On holiday in Bali 10 years ago, Kylie noticed a mole on his leg that he had assumed was nothing - he ended up having to head straight from the airport to the hospital to have a 21-centimetre melanoma cut out.

"I've never felt so embarrassed lying on a table saying 'yeah I've got a good suntan but it could have cost me my life'," he says. "Then I went and got a colonoscopy and all that stuff done. If my wife hadn't seen that melanoma I would be dead for sure. I would have left my three beautiful kids without a dad just through my ignorance. I realised ignorance is not bliss when it comes to male health checks."

He's now an ambassador for Cure Cancer and he trains hard and eats healthily. (He tells the Northern Beaches Review: "There's one side of cupboard which is the good side - protein bars and egg whites - and then there's my wife's side which is chips and chocolate and wine. The two seem to meet alright in the middle.")

"50 scares the hell out of me", he adds, noting that he hits 47 at the end of this year.

"I believe there's an old man always knocking on the door that doesn't want you to do things but you've really got to fight to get things done. At 47, once you stay 'I'm stopping for a while', that means you're stopping forever and you're never going back. You get old because you stop moving and then you lose muscle. That's when things go bad.

"Life is a continuous exchange of energy. I've got no intention of burning out. I'm going to rust out, not burn out."