According to Donovan, the footage captured the moment Irwin pulled the stingray's barb from his chest, before losing consciousness.
Since then, there's been speculation over whether the video should be released or not - with some fans claiming they've already seen it.
The Mirror reported that search interest in the footage "spiked" soon after the news of his death broke.
Donovan has said that Irwin wanted camera operators "to always be filming".
"If he needs help he will ask for it. Even if he is eaten by a shark or croc, the main thing he wants is that it be filmed," he recalled.
"If he died, he would be sad if no one got it on tape."
TV executives decided the footage was too shocking to air.
The Crocodile Hunter producer John Stainton said it was "very hard to watch because you're actually witnessing somebody die".
Members of Irwin's family and crew, as well as local police, are the only ones confirmed to have seen the footage.
"It shows that Steve came over the top of the ray and the tail came up, and spiked him here [in the chest], and he pulled it out and the next minute he's gone," Stainton said.
"That was it. The cameraman had to shut down."
At the time he called for the tape to be "destroyed", telling CNN's Larry King Live in 2006 "it will never see the light of day".
It comes after Irwin's daughter Bindi shared a sweet tribute to her father.
Bindi shared a moving tribute to her father on Saturday.
"Grandpa Crocodile, I know you would've been the most incredible grandfather because you were such an extraordinary dad," she wrote on Instagram.
Stainton said all copies of the tape had been destroyed, except for one given to Irwin's widow Terri, who reportedly destroyed it without seeing it.
