Fifty years after her death, an author who met the star has questioned her sexual identity.
Although she married and divorced three times, she was – though few people are aware of the fact – a lesbian by inclination.
She admitted to sexual encounters with actresses Joan Crawford, Barbara Stanwyck, Marlene Dietrich and Elizabeth Taylor, as well as with both her acting coaches, Natasha Lytess and Paula Strasberg.
Only a day before Jean Negulesco, who directed her in 'How To Marry A Millionaire', was due to visit her, Monroe was found dead.
"I still think I might have saved her if I could have got to her in time," the Daily Mail quoted him as saying.
"You know what was wrong with her, don't you?
"Her whole existence was a search for identity, and her sexual identity was a complete lie.
"She told me once she had never had an orgasm with a man in her entire life," he said.
And yet Negulesco's assertion is validated by the taped transcripts of Marilyn's sessions of psychoanalysis with her psychiatrist, Dr Ralph Greenson, at the end of her life.
"What I told you is true when I first became your patient," she says in the transcripts.
"I had never had an orgasm. I well remember you said an orgasm happens in the mind, not the genitals.
"When I did exactly what you told me to do, I would have an orgasm?...? what a difference a word makes.
"You said I would, not I could. Bless you, doctor. What you say is gospel to me," she said.
Another of those who worked with Monroe, actress Celeste Holm, who appeared with her in 'All About Eve', and who died last Sunday, said that Marilyn's sexual problems were rooted in her traumatic childhood.
Born illegitimately in 1926 to an unmarried mother in the charity ward of the Los Angeles General Hospital, she was originally known as Norma Jeane Mortenson, the child of a 24-year-old film negative cutter, Gladys Pearl Monroe Mortenson, who developed schizophrenia.
Both of Gladys's parents, Otis Elmer Monroe and Della Monroe Grainger, lived out their twilight years in mental institutions, while Gladys's brother, Marion, was diagnosed with paranoid schizophrenia.
So it is small wonder that the child who became Marilyn Monroe grew up with a deep-rooted fear of genetic insanity.
This, according to Celeste Holm, gave Marilyn a lifelong terror of pregnancy.
In addition to her fear of giving birth to an abnormal child, Marilyn suffered from devastating bouts of endometriosis, a gynaecological condition causing intense pelvic pain, severe cramps and painful periods.
It made normal sexual intercourse difficult and uncomfortable.
"Because of this Marilyn was never able to enjoy sex with men," Holm said.
"She was afraid of it, and turned to older women as sexual role models," she had said.
After Marilyn had become a world-famous sex symbol, her first husband, Jim Dougherty, who joined the Merchant Marine in 1943, would brag: "Never had I encountered a girl who so thoroughly enjoyed a sexual union. It made our lovemaking pure joy".
But this, sadly, was far from the truth.
"Jim told me privately that she spent most of their early marriage locked in the bathroom," Martin Evans, a friend of Jim's at the time they married," said.
"She had sex books and manuals that were given to her, and none of them made a difference.
"She was scared. From my information, she even asked if it were possible for her to never have sex with Jim. "Could they just be friends?" she wondered.
"To be honest, I don't think they had a good sex life ever – despite what Jim later claimed," he said.
According to Holm, for years Marilyn was in love with the idea of being Betty Grable – the Forties star known as the Girl With The Million Dollar Legs).
In 1969, Grable said me that she had found Monroe's pursuit of her 'sometimes scary, but you have to understand that all her problems had to do with her not being able to have a child.
Another female star Marilyn pursued and propositioned was Judy Garland, who married three gay men among her five husbands.
Shortly before Marilyn signed with Columbia Pictures in 1948, she met Natasha Lytess, a failed actress who was a drama coach at the studio.
"I want to recreate you. I shall mould you into the great actress I suspect you can be. But to do so, you must submit to me. Do you understand?" she told Marilyn.
In 1950, Marilyn moved into her apartment while she was being escorted by a new father-figure, the venerable Hollywood agent Johnny Hyde.
When Hyde died from a heart attack in December 1950, Natasha rescued Marilyn from a suicide attempt with a drug overdose.
Marilyn told her close friend, actor Ted Jordan, that she and Natasha were sleeping together.