The distinctive hooped necklace that she wore on Thursday was particularly fitting for what was, after all, an engagement celebrating the Olympics.
It also gave an added air of sophistication to the simple shift by Stella McCartney which the Duchess of Cambridge had picked out to visit an exhibition about the Games at the National Portrait Gallery.
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At £50,000 the Cartier Trinity Necklace is pricier than would be expected of Kate, who has developed a reputation for being prudent.
The 18-carat chain features pavé diamonds as well as three intertwined circles of pink, yellow and white gold.
It may well have been a gift for her recent 30th birthday from Prince William or her parents. But neither Cartier or her aides would be drawn into discussing who bought it.
A St James's Palace spokesman said of the necklace: "It's a personal piece which she's had for some time. It's not an official Olympic item but it's appropriate to wear it."
As the patron of the gallery and an ambassor for London 2012, Kate had been invited to unveil 100 new portraits related to the sports spectacular.
Subjects of Road to 2012: Aiming High include London Mayor Boris Johnson and Mark Cavendish, a cyclist who was the BBC's Sports Personality of the Year in 2011.
The sporty royal appears in the exhibition herself in a photograph by Jillian Edlestein of her training with Team GB hockey players earlier this year.
On that occasion Kate, who was the captain of her school hockey team, impressed with her athletic skills.
The Duchess, a History of Art graduate, also viewed other works including one showing footage of David Beckham asleep taken by Sam Taylor-Wood.
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