Steve – known as the Crocodile Hunter - was killed by a stingray in 2006 and his children Robert and Bindi have followed in his footsteps when it comes to wildlife and conservation.
In an interview shared with People magazine, Robert and William chatted ahead of the royal's Earthshot Prize awards.
And the prince told Robert, 17, that he had admired his late father, who operated Australia Zoo and was known for several TV series.
“Honestly, I was a big fan of your dad and I am so sorry,” Prince William said.
“It's no surprise that you're a fan of crocodiles as well. The family trait has continued into the next generation I am sure."
"He'd be very proud of you Robert,” he went on. “And what you continued. Your passion is only second to his."
Robert was only two when his father died after a stingray barb pierced his heart while he was filming a television programme.
He and his sister Bindi, 23, have continued his work and work at the Australia Zoo. They are also known for television shows such as Crikey! It’s The Irwins.
The Earthshot Prize launched by Prince William recognises those who come up with solutions to the planet's problems. It will see five, one million pound prizes awarded each year for the next ten years.
Watch: Prince William reveals why Shakira is involved in Earthshot Prize