One of the beauties of the Olympic Games is that it creates heroes. There are the predictable ones, like Jessica Ennis, Usain Bolt and Sir Chris Hoy, and then there are the less predictable ones, like Gemma Gibbons, Jade Jones and Gabby Douglas. But perhaps the most unlikely hero from London 2012 was not an athlete at all, it was an athlete’s father. Chad le Clos scored a dramatic, improbable victory over Michael Phelps in the 200m butterfly at the London Aquatics Centre but it was his dad, Bert, who really captured the imagination of the British public. The BBC’s Clare Balding spotted him going crazy in the crowd while watching his son and just a few minutes later, she had him at her side doing an interview. Balding barely spoke, she just let Bert talk and those few minutes became one of the abiding memories of London 2012. His emotional, proud and joyous reaction to his son becoming Olympic champion was utterly compelling and Bert became a star.

Matthew Pinsent has spent the past two years with the Le Clos family making a documentary that follows Chad’s journey to Rio as he attempts to defend his 200m butterfly crown. The programme is called ‘Unbelievable’ and what is even more captivating than Chad’s build-up to the Olympic Games is the view that we get of his family. A year into Pinsent’s filming, it was discovered that Bert had the early stages of prostate cancer. Then, devastatingly, three months ago, Chad’s mother, Geraldine, discovered that the breast cancer she had recovered from in 2010 had returned although they are both recovering and hope to be in Rio to watch Chad swim.

The initial plan, Pinsent has since said, was that Chad and the sport would be the central story line of the programme. And it is. But what is so engaging about Pinsent’s documentary is that it illustrates just how invested athlete’s families are in their careers. Athletes always trot out the line that they couldn’t do it alone and, of course, this is true. The most direct influencers on an athlete’s career are their coaches, physios, psychologists, nutritionists and the rest of the army who are charged with getting an athlete into peak mental and physical condition. But what is less highlighted is just how much families invest- yes, financially but, more importantly, emotionally in their son’s or daughter’s or spouse’s career.

In Pinsent’s documentary, he shows the Le Clos family home in Durban. Everything is set up in order to make Chad’s life as easy as possible. In the aftermath of London 2012, the family built an extension to the house for Chad to live in. Still only 24, Le Clos eats the food that his parents buy and gets his washing done by them. So far, so normal for a boy in his early twenties. Yet the Le Clos family eats when Chad wants to eat. And the entire household goes to sleep early because that suits Chad’s training schedule.

What is so interesting about the life of the Le Clos family which Pinsent documents so well is that almost every family that includes an elite athlete has similar stories. Bert’s reaction to his son winning gold in London was so endearing because it illustrated just how invested he was in every one of Chad’s swims. Every disappointment is felt just as piercingly by an athlete’s family as it is by themselves. Every victory is a joint victory.

There are few more stressful situations for an athlete’s family than watching them compete. God knows, I nearly killed mine more than a few times. There are many that cannot even bring themselves to watch. I ghostwrite a blog for 400m hurdler, Eilidh Doyle, for the Women’s Sport Trust and in her final pre-Rio installment, we were chatting about how her family feel about watching her. “They can’t,” she replied bluntly. At Glasgow 2014, where she won silver, her parents, sister and husband were all in Hampden stadium but they couldn’t bring themselves to watch her race. Her dad, she says, has barely been able to watch her compete since she was 13.

And that’s only the competition side of it. It’s the athlete’s family which has to pick up the pieces after a devastating defeat or try to keep morale up during injuries. In a funny way, being the athlete is the easy part. When you’re the athlete, it’s in your own hands. Whereas for the families, all they have to concentrate on is the impending nervous breakdown.

Over the next few weeks in Rio, dozens of British athletes will win medals, even more will return home disappointed. For every one of them, their families will be feeling exactly the same way, perhaps even more intensely. There may not be anyone who articulates their feelings in Rio as Bert le Clos did in London, but that doesn’t mean that they’re feeling it any less.