Hugh Hefner's Widow Demands Investigation Into Playboy Founder's Sex Diary

Hugh Hefner kept a sex diary full of lurid descriptions and thousands of nude images of his conquests, at least according to his widow ... and she's fighting to keep it all under wraps.

Crystal Hefner and her attorney, Gloria Allred, announced Tuesday they believe Hef's sex diary contains around 3,000 photos of women -- some possibly underage -- before, during and after sex.

Hugh is famous for his Playboy Magazine empire, but Crystal and Gloria says the scrapbooks are personal nudes and not photos that were ever shown in Playboy. They say Hef's alleged sex diary dates back to the 1960s ... with names of sexual partners matched with sex acts.

And, get this ... they say Hef even tracked some of his partners' menstrual cycles.

Crystal claims the sex diary and photos are waiting to be scanned and digitized by the Hugh M. Hefner Foundation ... but she says she didn't consent for any of her photos to end up in someone else's hands, and she's certain many of Hef's sexual partners fall in the same boat. Plus, she says she's gotten no clear answer from the foundation about where the diary is, which is also concerning.

Crystal had been the head of the foundation until Monday when, after expressing concerns over the photos and diaries, the board of the foundation removed her.

Gloria is calling on the Attorneys General of California and Illinois to investigate the alleged sex diary and keep all images and mentions private.