However, it was only a foretaste of the royal ring. That same month, her future girlfriend began shooting High Society (1956), her last film before getting married and having to abandon her acting career. In the film, a key version of Cole Porter’s musical comedy The Philadelphia Story, Kelly plays wealthy socialite Tracy Lord, who must choose between three very different amorous suitors.

Engaged to the wealthy but boring George (played by John Lund), Lord wears an all-star ring throughout the film, with a center stone elegantly flanked by a pair of tapered baguettes. And it wasn’t a fake ring for production. “We have photos of them looking at the windows of the Cartier store on Rue de la Paix (in Paris),” explains Pierre Rainero, Director of Image, Heritage and Style at Cartier. “I don’t know if they were already married or engaged, but maybe they chose this very ring,” and he adds that the jewelry store records the transfer of a ring from Paris to her shop in Monaco.

Be that as it may, the diamond found its way to Kelly’s ring finger and she ended up having a starring role on the big screen. In one scene, Bing Crosby, who plays Tracy’s ex-husband in the film, jokes about his size. In another, Kelly’s character polishes the massive stone on a cushion, then leans back to admire it.