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Hugh Hefner has learned a thing or two in his 84 years, like, for instance, how to string along a 24-year-old Playmate. Or so says the Chicago Sun-Times, which claims the twice-divorced Playboy icon is planning a really long engagement with newly minted fiancée Crystal Harris.

"Though in Hef's case," notes a source, "how long can that be?"

But should he find himself at the altar, you can bet his assets will be securely locked down before he promises to take Crystal for better or worse, in sickness and in health, until one of them (and we're not gonna guess which one) goes to that big Playboy mansion in the sky.

"That prenup will be tighter than Cher's most recent face-lift!" zings another snitch.

But has Hef's nuptial change of heart stung an ex? According to the paper, Holly Madison, Hugh's onetime girlfriend, is "very upset" by his betrothal.

"She can't believe Crystal was able to get Hef to agree to something she had tried for so long," sighs an insider.

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In her quest to settle down and have kids with the AARP-approved ladykiller, Holly stuck with him for seven years (and second banana "Girls Next Door" gal pals Kendra Wilkinson and Bridget Marquardt).

She pulled the plug in 2008, explaining, "It wasn't right for my old age. I got too old for Hef."

A few months before, the magazine mogul stated in no uncertain terms that Holly would never be Mrs. Hefner: "I love Holly very much and I think we're going to be together the rest of my life. But marriage isn't part of my puzzle. It's not a personal thing -- I just haven't had much luck with marriages."

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But hope springs eternal.

"[With Crystal], I have found the relationship that I thought I had found with Holly," he told FOX News in April. "In retrospect, I do believe in the most recent years, I was, without being aware of it, starting to look for a more serious one-on-one relationship. And when it did not work out with Holly, I was blessed beyond words to so quickly find someone who really just was waiting ... I'm in a serious relationship that I think is going to last -- with luck -- the rest of my life."

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