In the last five minutes of the Royal and Noble collection sale at Sotheby's auction house in London on Wednesday, a representative for Kardashian successfully outbid others vying for the amethyst cross.
The item sold for more than double its pre-auction estimate, Sotheby's said.
"This is a bold piece of jewelry by its size, color and style which cannot fail to make a vibrant statement, whether it be of faith or fashion — or indeed both," Kristian Spofforth, head of jewelry at Sotheby's London, said in a press release Wednesday.
"We are delighted that this piece has found a new lease of life within the hands of another globally famous name," Spofforth added.
Made by court jewelers Garrard in 1920, according to the auction house, the pendant features square-cut amethyst stones in the shape of a cross, decorated with circular-cut diamonds in a distinct flowery design.
The piece is about 5.4 inches by 3.7 inches in size, and has a total diamond weight of approximately 5.25 carats.
It was bought from Garrard in the 1980s by the late businessman Naim Attallah, who loaned the item to his friend, Princess Diana, several times to wear to events, according to Sotheby's.
Princess Diana "had a particular fondness" for the pendant, the auction house said, and she famously showcased it while wearing a black and purple Catherine Walker dress to a charity gala in support of Birthright, a charity working to protect human rights during pregnancy and childbirth, in October 1987.
The princess married the now British King, Charles III, in 1981, becoming an international icon who used her fame to raise awareness for numerous causes, including leprosy, HIV, domestic violence and mental health.
"Princess Diana's confidence grew during the 1980s as she became known for increasingly bold fashion choices, moving away from the more romantic and subdued style she had hitherto favored," said Sotheby's in the release.
"The fact that she is known to have worn what is now known as the Attallah Cross on several times -- mostly to private occasions, substantiates this evolution," it added.
The auction house understands that Diana was the only one to ever wear the cross, and this is the first time it has appeared in public since her death.
While this is a piece of British royal history, Kardashian famously wore a piece of Hollywood history to last year's Met Gala. The 42-year-old appeared on the red carpet in a sparkling skin-tight gown once worn by Marilyn Monroe when she famously sang Happy Birthday to President John F. Kennedy in 1962.
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