Hefner's health had been in serious decline over the last year and he's not been seen in public for some time.
His passing comes just over a year after his brother, Keith, died battling cancer.
then former Playmate of the Year Kimberly Conrad in 1989 ... He's survived by 4 children -- Christie and David from his first marriage and Marston and Cooper from his second marriage.
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And his pioneering magazine, his biggest legacy, may have helped the buttoned-up America of the 1950s and early 1960s loosen up a little about sex.
"I would like to be remembered as somebody who has changed the world in some positive way, in a social, sexual sense, and I'd be very happy with that," Hefner told CNN.