The famous blonde was subject to years of speculation over whether or not she had gone under the knife.
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The documents, dated 7 June 1962, just one week after her 36th birthday and two months before her death, were written by plastic surgeon Michael Gurdin and later gifted to a friend.
They refer to a cartilage implant in Marilyn's chin that he had inserted for a "chin deformity". Michael observed in the notes that the implant had begun to dissolve.
A facial X-ray, meanwhile, reveals a small fracture on her nose, fuelling speculation that she had a minor rhinoplasty early in her career.
The exclusive documents are now going up for auction with the Julien's Auction House in California. They are expected to fetch between £10,000 and £20,000.
"Nobody really thought about Marilyn Monroe having plastic surgery," said Martin Nolan, executive director of the auction house. "It was all speculation – did she or didn't she? They thought she was such a natural beauty, they didn't want to believe it."
Confirming the authenticity of the documents, Martin said, "Everything added up — the timeline, the dates, the names, the addresses. I can tell you the seller also had a close relationship to the doctor.
"They are a part of pop culture history," he added. "Worldwide, people have a love affair with Marilyn."