Bert said his son had set world records and won gold on a bigger stage – but the freestyle relay bronze medal in Glasgow was “as emotional as the first one”.
He added: “I realise that my little kid – who is now a pensioner – was unbelievable in what he achieved.”
In a wide-ranging interview with BBC Scotland, 69-year-old Bert said his life had been “revolutionised” by his son.
He recalled how Chad had prompted him to quit smoking when, at the age of 12, he asked his father to give up the habit instead of buying him a Christmas present.
Bert hasn’t had a single cigarette since that day.
The grandfather – who weighed 140kg (22 stone) at the time – also stopped drinking every day and lost 41kg (6.45 stone).
“He made me change my life,” said Bert.
“I would probably be dead now if I had continued the way I was. That’s a good lesson for other parents.”