She arrived at the glamourous event wearing the late star's $5 million gown, which she wore in 1962 to wish President John F. Kennedy a happy birthday.
Following weeks of speculation, the billionaire arrived wearing the iconic gown - complete with freshly dyed platinum blonde locks.
Walking the red carpet with boyfriend Pete Davidson, Kim revealed that she had to lose 16 pounds to fit into the dress, opting to forgo carbs and sugar for three weeks.
Blake Lively also walked the carpet, stunning in a pink gown that transformed to blue. Lively's dress and jewelry were inspired by New York City architecture. Kim made history by being the only person besides Marilyn to dress in the iconic gown in the 40 years since it was produced.
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'This is Marilyn Monroe's dress. It's sixty years old. I had this idea to put it on and try it on. They came with armed guards and gloves. I tried it on, and it didn't fit me. I had to lose 16 pounds,' Kardashian exclaimed on the red carpet.
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'I was determined to fit it... I did it...' adding that she hasn't eaten carbs or sugar for three weeks and also dyed her hair blonde.
For weeks, fans speculated that Kim would wear Marilyn Monroe's $5 million gown, last worn May 19, 1962.
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The dress was created from a sketch by Bob Mackie for the costume designer Jean-Louis; the translucent gown features over 6,000 crystals. Marilyn reportedly paid $1,440 for the custom piece and in 1999, her estate sold it at an auction for over one million dollars, per Vogue.
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It once again switched hands when it sold in 2016 for $4.8 million before Ripley's Believe It Or Not Museum acquired it.
Per the outlet, the dress resides on a muslin-covered dress form at the museum in a darkened vault at a controlled temperature of 68 degrees with 40-50% humidity.
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Last month, she was photographed leaving Ripley's Museum in Orlando, where the dress is housed, spurring fans' belief that she would wear it. During the premiere of the Kardashians last month, she revealed that she might not attend because she has to fit in the dress since it cannot be altered.
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In an interview with Vogue, Kim informed the magazine that the idea came last fall at last year's Met Gala. 'The idea really came to me after the gala in September last year. I thought to myself, what would I have done for the American theme if it had not been the Balenciaga look? What's the most American theme you can think of? And that's Marilyn Monroe,' she told Vogue.
'For me, the most Marilyn Monroe moment is when she sang, "Happy Birthday" to JFK, it was that look.'
'Nowadays everyone wears sheer dresses, but that was not the case back then. In a sense, it's the original naked dress. That's why its so shocking,' she revealed to the magazine.
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The mother of four revealed she had dyed her raven tresses platinum one day prior, in a process that lasted 14 hours.
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Kim connected to Ripley's via the owner of Julien's Auctions, noting that she also loves auctions and owns several JFK pieces.
Before the museum allowed Kim to borrow the piece, they allowed her to try a replica which fit; the next step was the original gown getting flown to California from Florida for her to try on.