Quincy Jones has made some bold dating claims lately, but this one takes the cake ... he says he used to date Ivanka Trump, who he remembers as being pretty damn hot.

The music legend says he and President Trump's daughter hooked up -- meaning, dated -- about 12 years ago after Tommy Hilfiger told him Ivanka wanted to have dinner with him.

He tells Vulture he jumped at the opportunity, telling Tommy ... "'No problem. She's a fine motherf*****.' She had the most beautiful legs I ever saw in my life. Wrong father, though."

Q said he used to hang with Ivanka's dad too, but his memories were not nearly as fond -- "He's a crazy motherf***er. Limited mentally -- a megalomaniac, narcissistic. I can't stand him."