A West Coast father whose son drowned after his car flipped upside down in a pond only crashed because he had a brain tumour, his close friend says.
Mark Bowes' son Tayne, 9, drowned after the Toyota Hilux they were travelling in flipped upside-down in a waist-deep mine pond about 12 kilometres south of Hokitika on August 12.
His 8-year-old sister, Keira, survived after spending nearly two hours in water in the submerged vehicle.
Barry Foster, who has known Bowes for over 25 years, said his friend had a brain tumour, which he believed had caused the crash.
''There wouldn't have been an accident if he hadn't had this tumour. None of this would have happened. I know that 100 per cent,'' he said.
''When I heard about the accident I said to my wife: 'Mark must have had an epileptic fit or something. I knew something was wrong'.''
Foster said Bowes was in the car at the time of the accident, but could not remember anything that happened.
''He doesn't know what happened. He said the handbrake was on and we think he may have had a seizure and Tayne pulled it on. He desperately wants to know what happened, but he can't remember at all.''
After the accident, Bowes was confused and ran from the scene before calling police. Keira was then rescued by police officers.
''He ran at random until his feet were bleeding. He had no idea what he was doing.'
Foster believed both children could have been rescued if Bowes had been in his ''right mind''.
''He would have ripped the door off to save those kids - that's the kind of man he was. He was a strong guy and would have done anything to get to them. There's no way he would have run off."
There had been no signs of a tumour prior to the accident, but in the week following the tragedy, Bowes couldn't stand up or speak properly.
''For the whole week he couldn't stand up and was slurring his words. At first we thought he may just have taken a hit on the head in the accident,'' Foster said.
Bowes went to see his doctor on the coast, who referred him to Christchurch Hospital for an MRI scan.
''They found there was a tumour pressing on his brain. They operated to remove the tumour and he's going to start radiotherapy in October,'' Foster said.
''After the surgery I went to see him and he said he was going to see his little boy. He doesn't give a stuff about the tumour or want surgery; he just cares about the family he's left behind."
Foster said Bowes had faced unnecessary criticism from the public after the accident.
''Without the information people have been drawing their own conclusions as they did. I read something that compared him to the Kahui twins and I knew I had to say something. He is not a bad guy.''
Bowes could not move on from the loss of his son, Foster said.
''He's absolutely devastated, especially that he doesn't know exactly what happened. I said to him it could have been much worse. He could have been driving down Arthur's Pass when this happened and hit a logging truck and the whole family could have died. It's a miracle Keira is still alive.''
It would be Tayne's birthday on Saturday and family and friends would be gathering on the West Coast for a rugby game as a tribute to the rugby-keen boy.
''We will all be there and try to move on from the accident, but it is tough on the whole family,'' Foster said.