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Tonight is the annual Costume Institute Gala at the Metropolitan Museum of Art in New York, better known simply as the “Met Gala.” More than two decades ago, the gala had a guest with a bit of royal star power: Diana, Princess of Wales.

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The December 1996 gala honored the work of Christian Dior, and Diana followed the theme, wearing a dark blue gown by John Galliano, then the creative director of Dior. The navy slip dress was made of silk and featured black lace detail. She also carried a navy bag from the brand.

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Diana attended the event with her friend (and Harper’s Bazaar editor), the late Liz Tilberis. Although 1996 was a rather minimalist era in the fashion world, Diana did wear two major pieces of jewelry to the gala. Her earrings feature a sapphire and diamond cluster stud and a slightly larger cluster drop. (Many have speculated in the past that these earrings were the source of the Duchess of Cambridge’s sapphire cluster earrings, but the pieces are not the same.)

She also wore her iconic seven-stranded pearl choker necklace with the enormous sapphire and diamond clasp. Above, you can see that the necklace was featured about a year later in a set of stamps that commemorated Diana’s life. The piece was the largest item of jewelry that she continued to wear in public following her separation and divorce.

The huge sapphire and diamond cluster clasp was originally a brooch; Diana had it converted to a necklace clasp in the 1980s. The necklace’s most famous outing came in 1985, when Diana wore it while dancing with John Travolta at the White House. The sapphire was a wedding gift to Diana from the Queen Mother, and she kept it (and wore it) after her divorce. We don’t know exactly what happened to this magnificent jewel after her death; it’s possible that it remains in a collection of items now owned by her sons, William and Harry.