A father's dilemma: three events, two sons and only one winner as Alistair and Jonny Brownlee prepare for Olympic triathlon

Bert le Clos, the father of the South African swimmer Chad, showed how overwhelming the Games can be for Olympic parents when he made an emotional tribute to his "beautiful boy" on live television last week.

Spare a thought, then, for Dr Keith Brownlee, the father who has not one, but two sons going for gold in London tomorrow. To make matters even more nerve-shredding, they're competing in the same race.

The story of the fabulous Brownlee boys, Alistair and Jonny, Britain's top two triathletes, is the stuff of sporting fairytale. Tomorrow the brothers, who not only grew up together, but train together and live together in Leeds, go head to head in one of the Games' most gruelling events.

"We saw them on Thursday night and we won't be seeing them again before the Games," Dr Brownlee told The Independent. "All I said was: good luck and do your best."

Alistair, 24, the elder of the brothers, is also the most hotly tipped for Olympic glory, but Jonny, 22, is never far behind. At the Kitzbühel triathlon at the end of June, Alistair came first and Jonny second. At an event earlier that month in Oxfordshire, the gap between the brothers was so tight that they decided to cross the finish line arm-in-arm.

Alistair has the experience of a previous Olympics to lean back on, having come 12th in Beijing four years ago. For Jonny, it was the experience of watching his brother qualify for those Games that persuaded him to train as a triathlete himself.

"They have always been competitive, in everything they did," their father recalled. "Be it monopoly, chess, who would get up earliest ... anything."

Now their chosen field of combat is somewhat more demanding. Tomorrow's triathlon will begin with a 1,500m swimming race in the Serpentine in Hyde Park, followed by a 43km cycle race and a 10km run to the finish line. It is not for the faint-hearted.

"It was a gradual progression for them to get where they are now," said Dr Brownlee.

The man with the best chance of upsetting the party is Spain's Javier Gomez, but the prospect of a shared podium is becoming very real for the Yorkshire family. "They have been supportive of each other. They both recognise that neither would be where they are without the other," said Dr Brownlee. "I try and persuade them to think about it as a family business."

Their dad isn't letting himself get carried away, but he says he can "absolutely" relate to how Mr Le Clos must have felt watching his son win gold at the Aquatics Centre last week.

"To see that was fantastic," he said. "It's very difficult to describe what I feel. Kathy (the boys' mother) and I both just want them to finish the race healthy, intact and content. We're so proud that they've got this far. What comes next doesn't matter."