She added that he was a strong swimmer who had competed six times in the physically tough Ironman triathlon.
“Rest in peace, Paul,” she said.
Mr Millachip is believed to have been taken by at least one 14ft (4.5m) shark, about 50 metres off Port Beach, north of the popular surfing spot Sandtrax. His wife was in Port Beach’s changing rooms at the time while his two adult children were also at the beach.
Witnesses said they saw him struggling in the water before being “dragged under”.
Land, air and sea patrols conducted over the weekend yielded no results.
On Saturday, WA Police Senior Sergeant Troy Douglas said the incident was witnessed by four teenage boys in a dinghy just metres from the attack.
“They [saw] what was going on in the water … a person being attacked by a shark… And they have alerted emergency services straight away,” he said.
Police and witnesses said the boys were heroes for getting people out of the water so quickly.
Mr Millachip’s wife said their actions were “amazing,” and that it must have been an “absolutely terrifying experience”.
“[They] could have potentially saved other lives,” she said.
“My heart goes out to them and I thank them for what they did,” she added.
Kaiden Boult, 16, told local media he and his friends had been surfing when a boy in a dinghy “came flying at us” screaming to get out of the water because there had been a shark attack.
The beaches were still sealed off on Sunday but were reopened on Monday.
“A family is now grieving, a man has lost his life. It’s a terribly sad situation,” West Australia Premier Mark McGowan said.
Talking on Today this morning, shark expert Darryl McPhee from Bond University in Queensland, said waters off Perth were a hotspot for shark attacks.
“Going forward, we still expect more fatalities over time. You just can’t exactly predict where and exactly when,” he said.
Last year saw eight fatal shark attacks in Australia. This year there have been three.
Locals and scientists point as the cause to warmer waters due to climate change, depleted fishing stocks and a domestic tourism boom triggered by Covid-19.