The pair played lovers in 1967 movie Camelot and director Joshua Logan was hoping for an on-set romance to boost the couple's chemistry.
But when the filmmaker first pointed Redgrave out to his Lancelot, Nero felt sure the wrong woman had been cast as the alluring Guenevere.
He recalls, "I see this woman who is wearing blue jeans with holes, glasses and no make-up. I was sort of cold when he introduced us.
"I said later, 'Josh, are you sure you got the right actress? She's ugly!' He said, 'Don't worry, you'll see.' I was a young Italian boy who thought women had to be dark like Sophia Loren."
Nero was in for a shock the next time he saw Redgrave, after she invited him to join her for dinner.
He tells the Los Angeles Times newspaper, "I knocked on the door and a lady opens the door. She was a beautiful lady. Fantastic. I said, 'I was invited here by Vanessa Redgrave for dinner. She said, 'I am Vanessa Redgrave!' She was completely changed. Unbelievable."