Hugh Hefner's longtime secretary, Mary O'Connor, dies

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"Girls Next Door" fans will remember Mary O'Connor as the Playboy Mansion's down-to-earth voice of reason. She maintained close relationships with both the staff and Hugh Hefner's ever-changing circle of girlfriends. After working as the "Playboy" founder's secretary for more than 40 years, O'Connor passed away Sunday.

"Mary passed away today. We loved her more than words can say," Heftner tweeted late Sunday night.

Mary passed away today. We loved her more than words can say.

— Hugh Hefner (@hughhefner) January 28, 2013

Hefner's new wife, Crystal, and former "Girls Next Door" stars Bridget Marquardt, Kendra Wilkinson and Holly Madison also shared their condolences.

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.

— Crystal Hefner (@CrystalHarris) January 28, 2013

Rest In Peace Mary! “@ashleymatthau: Just saw a rainbow! twitter.com/AshleyMatthau/…”

— Holly Madison (@hollymadison) January 28, 2013

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. :)

— Kendra Wilkinson (@KendraWilkinson) January 28, 2013

Thank you for all the sweet messages. Mary O'Connor will be missed. #RIPMary

— Bridget Marquardt (@Bridget) January 28, 2013

Though O'Connor's cause of death is not yet known, Hefner had tweeted about the eighty-something's poor health earlier Sunday.

Crystal is going to visit Mary O'Conner, who is not doing very well. Mary has our prayers. We all love her.

— Hugh Hefner (@hughhefner) January 27, 2013

Hefner is taking O'Connor's death "extremely hard," according to TMZ. Mary was reportedly known as "the rock" of the Playboy Mansion.

O'Connor's straight-talking yet welcoming personality is on full display in the clip below, in which she invites Hefner's girlfriends to her house for dinner.