Steve Begley was taken ill during the swimming event in the competition, which also involves long-distance running and cycling.
He was pulled from the water but paramedics were unable to save him.
Mr Begley, who was in his early forties, was a member of the Glasgow squad when the team turned professional in the mid-90s.
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Mr Begley, who was single, moved to Singapore 10 years ago to pursue his career in the financial services industry.
Steve was the first guy I met when I arrived from New Zealand in 1996. He was one of life’s fun guys
Yesterday, tributes poured in for him from friends and former team mates.
Ex-Scotland World Cup ace Glenn Metcalfe, who played alongside Mr Begley, said: “I was so sad when I heard the news. Steve was the first guy I met when I arrived from New Zealand in 1996. He was one of life’s fun guys.”
Hawks’ president Chas Afuakwah said “The news was hard to believe. Steve had just taken up rugby again after a spell out of the sport and he had taken part in several triathlons.
“I gather he had done one stint of swimming and had then done the running part of the competition. There was a second swim and it was when he was back in the water that something happened.
“The thoughts of everyone in the rugby community are with his family.”