Soon afterwards, Stuart pulled over and indicated for his nephew to go around him and continue on.
Nigel called him on his hands-free mobile phone to make sure everything was alright and the two men were talking when the phone suddenly went dead.
"He thought, 'okay, I've lost service, I'll contact him later'. But he carried on down and past a fire engine and cops racing up."
It was thought Stuart had been speaking to his nephew at the moment of the crash.
Prior to departing from Picton, he had complained of having sore legs.
"We know he has medical problems - he's a diabetic type 2 and he had cellulitis in his legs," Mervyn said.
"My theory is that perhaps he hit the left hand side of the bank to try and slow the truck down or stop it because he could feel something coming on medically, and he's bounced off that and gone over.
"The only thing I hope is that he was dead before he went over."
Stuart had been driving trucks for about 40 years and had a blemish-free safety record.
"He's never had a speeding ticket, he's never had a fine, he's never lost a load, he's never been caught for insecure loading," Mervyn said.
"He was a very professional man. He's driven that road more times than you've sat down and had hot meals."
He lived in Auckland and had a son and a stepdaughter.
"He was a no-nonsense guy - if you were a prick he'd tell you straight to your face, no pissing around," Mervyn said.
"He was a genuine guy that would help anyone. There wasn't a vicious bone in his body."
