But during his darkest days, Ken drew strength from the courage Aaron showed when confronted by his own major health scare two years earlier.

After completing a race in Spain in 2013, the world under-23 triathlon champion coughed up blood. He was promptly transferred to a hospital isolation ward, when doctors informed him in broken English that he had a 12-millimetre cyst on his lung, which was possibly cancer or tuberculosis.

To his immense relief, a biopsy revealed he was instead suffering from pneumonia, and three months later a top-six finish in a world series race clinched his berth in Australia’s team for the Glasgow Commonwealth Games.

On Thursday (at midnight AEST), the 26-year-old from Maryland will make his Olympic debut in Rio, with parents Ken and Kim and brother Nathan cheering him on in the crowd. Ken finished his chemotherapy treatment 12 months ago and received an “all clear” prognosis just a fortnight ago.

But he admitted that “most definitely” there were days when he doubted if he would be around when Aaron realised his Olympic dream. 

“Probably what inspired me was how Aaron fought back from that time when he was in hospital and they thought he had cancer or tubercolisis, and 12 weeks later he qualified for the Commonwealth Games,’’ Ken said.

“That was always in the back of my mind, to fight. I was just determined.’’

Ken said it would be another four years before he was considered completely in remission, and until then “you just have to keep batting on’’.

Ken and Kim arrived in Rio on Monday for the biggest race of Aaron’s career.

Before leaving, they had to juggle logistics to ensure the family fruit-and-vegetable delivery business, freshtoyou.net.au, ran smoothly in their absence.

Having pre-qualified for the Olympics a year in advance, after a top-10 finish in the test event, Aaron has spent the past few months training intensively in Vittoria, Spain. The Australian triathlon squad – comprising three men and three women – flew to Rio last Sunday.

Royle will race in Rio confident of challenging for a medal, after placing third in his most recent world series event, held in Leeds in June.

On that occasion he was beaten by English brothers Alastair and Jonathan Brownlee – the gold and bronze medallists at London 2012, and finished ahead of Spain’s multiple world champion Javier Gomez Noya, the Olympic silver medallist four years ago.

“He’s ranked in the top 10 in the world, so he’s going to be in there fighting,’’ Ken said. “I know one thing for sure, he won’t leave anything in the tank.’’

Royle is the second product of Maitland Triathlon club to represent Australia at an Olympics, after Brendan Sexton finished 35th in London.