Ripley's Believe it or Not purchased the Jean Louis designed dress covered in sequins, the Beverly Hills-based Julien's Auctions said in a statement.
With its color matching her skin tone, the dress, which was so tight that Monroe had to be sewn into it, gave the impression she was nude.
"Marilyn Monroe singing 'Happy Birthday Mr. President' is certainly one of the most famous impromptu performances in American history," said Darren Julien, President and CEO of Julien's Auctions.
Monroe, one of the 20th century's most famous sex symbols, wore the dress as she sang "Happy Birthday to You" to Kennedy in a breathy performance at a May 19, 1962 fundraiser for the Democratic Party in Madison Square Garden in New York.
The star of the films "Some Like it Hot" and "Gentlemen Prefer Blondes" died of a drug overdose less than three months later. Monroe's song was to mark Kennedy's 45th birthday, which was to occur a couple weeks later. The president was assassinated the following year.
The late fund manager Martin Zweig bought the dress in 1999 for $1.26 million at a Christie's auction, Julien's Auctions said. Zweig, who saw the dress as an investment, kept it in a climate-controlled display case mounted on a mannequin, Julien said.
The dress is one of many items from Monroe's life which Julien's Auctions is offering during a three-day auction. Monroe would have been 90 years old this year.
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