The most famous rendition of “Happy Birthday” is Marilyn Monroe’s version that she sang to President John F. Kennedy. But just as famous as her breathy take on the song is the tight, slinky dress she wore that caused a huge sensation.

The birthday celebration, on May 19, 1962 (10 days before his actual birthday), was at Madison Square Garden and was also a fundraising gala for the Democratic Party. More than 15,000 people attended, including numerous celebrities.

Taking the stage fashionably late, Monroe removed her white fur coat — to a slight gasp from the audience before it was realized that she was really wearing a skintight flesh-toned gown — and delivered the performance regarded as “one of the most iconic moments in entertainment and political history." Monroe’s sultry tone and the revealing nature of her outfit fueled rumors that she and the president had a secret affair.

Marilyn Monroe singing "Happy Birthday" to President John F. Kennedy at Madison Square Garden.

Marilyn Monroe singing "Happy Birthday" to President John F. Kennedy at Madison Square Garden.

Featuring 2,500 hand-stitched immensely sparkling crystals, the iconic marquisette dress was so tight that Monroe was unable to wear anything beneath it and had to be sewn into it by the designer moments before she took to the podium.

Marilyn Monroe's iconic "Happy Birthday" dress that sold at Julien's Auctions for a world-record $4.8 million.

Marilyn Monroe's iconic "Happy Birthday" dress that sold at Julien's Auctions for a world-record $4.8 million.

The back view.

The back view.

The dress was custom-made by renowned French fashion designer Jean Louis, who had worked with Monroe before and whose talents had earned him an Academy Award for Best Costume Design. It was based on a sketch by legendary American fashion designer Bob Mackie when he was 21 years old and at his first job with Louis right out of school. It was inspired by stage costumes Louis created for Marlene Dietrich and her Las Vegas cabaret act during the 1950s and '60s.

Designer Bob Mackie's sketch of the dress.

Designer Bob Mackie's sketch of the dress.

A closer look at the hand-sewn crystals.

A closer look at the crystals that were sewn on by hand, one by one.

Monroe paid $1,440 for the dress, about $12,400 in today’s dollars. In 1999, it sold at Christie’s as part of the landmark Marilyn Monroe Estate sale, where it fetched $1,267,500, setting a new world record price for any dress sold at auction. In 2016, the dress broke that record after selling at Julien's Auctions for $4.8 million. It was acquired by Ripley’s Believe It Or Not Museum, where it remains today. It also beat the previous record for a Monroe-worn dress, the iconic halter dress from The Seven Year Itch, which sold in 2011 at Profiles in History, as part of the renowned Debbie Reynolds Collection, for $4.6 million.

The historic "Happy Birthday" dress at Ripley's Believe It Or Not in Hollywood in 2018.

The historic "Happy Birthday" dress at Ripley's Believe It Or Not in Hollywood in 2018.

Marilyn Monroe wearing the former world-record dress in The Seven Year Itch on the streets of New York. When she stopped filming this famous scene over the subway grate, she posed for the reporters and photographers who were covering the film shoot.

Marilyn Monroe wearing the famous and former world-record dress in The Seven Year Itch on the streets of New York. When she stopped filming this famous scene over the subway grate, she posed for the reporters and photographers who were covering the film shoot.

“The dress is so much more than just an item of clothing,” said Martin Nolan, executive director of Julien’s Auctions, before the sale in 2016. “It’s historical, it’s political, it’s a work of art. It’s Hollywood, it’s Marilyn Monroe. It’s the Kennedys. It’s everything wrapped up into one piece of fabric soufflé gauze ... This dress, this story, this momentous occasion represents a defining moment in history."

Nolan and Mackie discuss the dress and Monroe in this 2016 YouTube clip.

Marilyn Monroe in the dress she wore to sing for President John F. Kennedy, pictured with his brother-in-law Steve Smith, left, at a party after the event.

Marilyn Monroe in her famous dress, pictured with President Kennedy's brother-in-law Steve Smith, left, at a party after the event.

“ … it was Marilyn who was the hit of the evening,” read TIME’s 1962 recap of the event. “Kennedy plainly meant it when he said, ‘I can now retire from politics after having had ‘Happy Birthday’ sung to me in such a sweet, wholesome way.’ ”

The performance was one of Monroe’s last major public appearances before her death less than three months later on August 4, 1962.

In this clip of Monroe serenading President Kennedy, you can see all of those hand-sewn crystals in action, glittering around her like thousands of tiny stars: 

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