Ross, 66, screeched with delight as Williams surprised her on Oprah Winfrey’s chat show.
“Are you kidding me? Are you kidding me?” the singer asked Winfrey as her former co-star appeared from behind the scenes.
She then ran up and hugged Williams, 73, before grabbing hold of his hand.
Asked what he remembered most about working with the former Supremes songstress, Williams cheekily said: “Her mouth.”
Ross, meanwhile, said that Williams was just as suave off camera as he was on screen.
“Every time he would go to kiss me, Barry Gordon would drag me away and say ‘That’s enough’,” she laughed.