The retired Perth vet who helped rescue 12 boys and their coach from a flooded Thai cave was pessimistic the massive effort would be successful, his partner says.
Craig Challen was packing to go on a holiday to the Nullarbor with his diving buddy Richard "Harry" Harris on Thursday last week when his friend called and changed their plans.
The pair were on their way to Thailand within an hour.
"I did express some concerns, obviously, but he was pretty adamant," Heather Endall told ABC radio.
"There was no talking him out of it."
She said he was delighted with the outcome but initially doubted the huge undertaking would end well.
"He did hold concerns for the whole situation," Ms Endall said.
"I think he went over there with a bit of a pessimistic view - he thought it was going to be a real challenge to get the boys out alive.
"He didn't actually display any regard for his own safety."
On their return to Australia, Mr Challen and Dr Harris would likely "sneak off to the Nullarbor and go down a cave to hide from the media", she joked.
Mr Challen co-founded the Perth veterinary franchise Vetwest but retired from the profession last year and now describes himself online as a dilettante.
He is part of a group of intrepid cave divers called the Wet Mules, as is Mr Harris, who loves to take photos and capture videos of their underwater adventures.
Mr Challen has explored Australia's longest and deepest underwater caves, Cocklebiddy and the Pearse Resurgence, and is one of only a few to dive some of the country's deepest wartime wrecks.
Prime Minister Malcolm Turnbull told the ABC that Dr Harris had spoken of the extraordinary heroism of the boys and divers, which would stay with him.
"I am inspired by the remarkable international cooperation," Mr Turnbull said.
"You know, you look around the world there's a lot of tension. What an extraordinary thing."