The television personality and conservationist, who became world-famous for his daring stunts with dangerous animals, died aged 44 in 2006 while filming a documentary on the Great Barrier Reef in far north Queensland.
Justin Lyons was the cameraman at the time and shot video of the tragic death, which was later handed to Irwin's widow, Terri, and has never been aired.
In his first public comments, Lyons told Australia's Channel Ten he and Irwin had left their main boat in an inflatable dinghy to find something to film when they came across a "massive" 2.5-metre wide stingray in chest-high water.
The final shot was to be the stingray swimming away from Irwin. Instead, the stingray struck out, apparently believing Irwin's shadow was a tiger shark, one of its predators.
"I had the camera on, I thought this is going to be a great shot, and all of sudden it propped on its front and started stabbing wildly, hundreds of strikes in a few seconds," Lyons said.
"I panned with the camera as the stingray swam away and I didn't know it had caused any damage. It was only when I panned the camera back that I saw Steve standing in a huge pool of blood that I realised something had gone wrong."
He said reports that a barb had stuck in Irwin's chest and he pulled it out were wrong.
"It's a jagged barb and it went through his chest like a hot knife through butter," he said.
"He had a two-inch-wide injury over his heart with blood and fluid coming out of it and we had to get him back to the boat as fast as we could," Lyons added.
"I was saying to him things like, 'Think of your kids, Steve, hang on, hang on, hang on', and he calmly looked up at me and said, 'I'm dying', and that was the last thing he said."
Stingrays have several sharp and venomous barbs on their tails that they use to defend themselves when they feel threatened, though experts at the time stressed that stingrays were not usually vicious and rarely attacked and killed humans.