Hugh Hefner's secretary of over 40 years has died.

Mary O'Connor, who appeared in reality show 'The Girls Next Door', passed away this weekend due ongoing health issues and Hugh, 86, is finding it ''extremely hard'' to come to terms with her death, TMZ reports.

The Playboy magazine mogul tweeted on Sunday (27.01.13): ''Mary passed away today. We loved her more than words can say (sic)''

Hugh's wife Crystal Harris, 26, also took to her Twitter account to pay tribute to Mary, saying: ''Hef's long time secretary & my dear friend Mary O'Connor has passed away. It's a very sad day here at the Playboy Mansion. We love you Mary (sic)''

His ex-girlfriend and 'The Girls Next Door' star Kendra Wilkinson wrote: ''RIP Mary O'Connor. She was an amazing person who helped me through so much. But I know she's happy with her boo Captain Bob. :) (sic)''

Bridget Marquardt thanked fans for their support at her time of grief, writing: ''Thank you for all the sweet messages. Mary O'Connor will be missed. #RIPMary(sic)''

Mary, who is believed to have been in her 80s, was described as ''the rock'' of the Playboy Mansion in Beverly Hills and everyone in the house is ''incredibly sad'' at the loss of such a well-loved member of the family.

Hugh previously praised Mary for helping him and Crystal reconcile after the blonde beauty called off their wedding in 2011.

He said: ''It's Mary O'Connor that brought Crystal Harris back. Crystal was miserable and said so. Mary told Crystal to write and tell me, which she did.''

The couple tied the knot at the Playboy Mansion on New Year's Eve (31.12.12).