Despite attaining this glorified status, Madison was treated anything like number one by Hefner.
She was subject to manipulation and degradation under the hands of Hefner and the other girlfriends in the house.
In her brazenly honest memoir, The Vegas Diaries, Madison reveals the truth behind a mansion known for sex and partying.
“Those people who watched The Girls Next Door…they thought I was happy with Hef,” she writes. “Hef painted it like some sort of fairy tale.”
“They think living at the mansion must have been heaven on earth,” the now 36-year-old admitted.
Holly for Hefner's 83rd birthday. Image via Getty.
Madison first moved to the Playboy Mansion from a small town in Alaska. Her name was Holly Sue Cullen and she was transfixed by the fantasy of the mansion after attending one party.
"All I had seen, before I became a girlfriend, was the other women making it sound like they loved it there, which I believed, because Hef had the perfect gentlemen act down pat."
But, Hefner was just exactly that - an act.
"He [Hefner] knew roughly four things about each girl: her name, her age, where (approximately) she was from and how well she behaved and followed the rules.
"He liked to play favourites to keep everyone on their toes. How else could he stay in control of seven women? He needed to somehow maintain the upper hand."
Madison wasn't the only one to experience this type of treatment, and many of his girlfriends were forced to extremes to deal with it each day.
"I was feeling so insecure, I did the only I could think of to help me get through the night - I'd drink. We all routinely turned to drinking out of boredom or to escape our demons."
Among other things, Madison was forced to sneak around the mansion just to avoid Hefner and would talk to animals.
But Hefner also wasn't the only one who victimised Madison in the house. Apparently, all the girlfriends were against one another.
Madison describes the other girlfriends as a "vicious horde of girls" who were never nice to one another.
What many may wonder is why Madison never tried to get help in the situation, but it's far harder to deal with the situation when you're in it.
Check out Holly's life now. Images via Instagram. (Post continues after gallery.)