The 39-year-old former glamour model was left devastated by the news that the publishing magnate had sadly passed away at the age of 91 from natural causes and, almost immediately, dug through her extensive archive of photo shoots to find three raunchy covers she shot for Playboy magazine - founded by Hefner in 1953 - in 2002 and then again 2004 as her alter ego Jordan.
Alongside a photograph of her cuddling up to Hefner when she lived at the famous Playboy Mansion, she simply wrote: ''RIP Hugh Hefner.''
She then added another picture of her enjoying a flute of champagne with the businessman in a skimpy bralette and accompanied it with the caption: ''What sad news this morning of this lovely man. Great times.''
Her third and final post was a three-picture collage of her covers - including two of her topless - with the caption: ''My Playboy covers.''
Katie shot her first cover for the promiscuous magazine when she was just 24 - shortly after she agreed to move in with the businessman.
However, rather than sleep with him, the blonde bombshell decided to make her mark by urinating in the lavish property's infamous grotto.
She said recently: ''When I was younger I lived with Hugh Hefner at the Playboy Mansion for about six weeks, but to be a girlfriend you have to do the deed and I did not want to do the deed.
''He's a really nice guy though. I just didn't want to do it. But I went to the famous grotto and I marked my territory - I p***ed in it.''
And, although her glamour modelling days are behind her since she's become a mother to her five children; Harvey, 16, Junior, 12, Princess, 11, Jett, three, and Bunny, two, Katie wants to pose for Playboy again.
She said: ''I can see myself going on until I am old - and I mean old. I keep saying to myself that I want to, when I'm 70, pose for Playboy. I will have the best boobs - even then, they'll be better than any other Playboy model's - and my bum won't be bad either.''
Meanwhile, a representative for Hugh announced that he'd passed away from natural causes at the Playboy Mansion in Los Angeles, California, surrounded by his loved ones.
He leaves behind his third wife, Crystal Harris, a former Playboy Playmate who he married in 2012.
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