The Black Sabbath rocker got in touch with the comedian after his Tv star partner was diagnosed with colon cancer because he was convinced the actor, who played a doctor in 1998 movie Patch Adams, would be able to put a smile back on Sharon's face.
Williams turned up at the couple's home in the morning and climbed into bed with Sharon as a joke, and Ozzy admits he will never forget the actor's generosity.
He tells the Vh1 Radio Network, "I'm forever in debt to Robin Williams, because when Sharon was diagnosed with colon cancer, I'd seen the film Patch Adams... it's about a guy who was a male nurse or something in a hospital and he was working with terminal people, and I thought, what a great thing to do, and he's a very funny man, Robin Williams. I got my agent to contact him and ask if he'd be so kind as to come around and talk to my wife, which he did. It was very nice of him."
Williams was found dead on Monday (11Aug14) in a suspected suicide.