Kate was in attendance with Prince William, 37, at the annual Diplomatic Reception at Buckingham Palace.
The reception was attended by members of the Diplomatic Corps based in London — who support the work of the royal family, including the hosting of state visits and the Queen's regular audiences with ambassadors and high commissioners.
There she showed off what is thought to be a new diamond ring on her right hand - an early Christmas present from William maybe?
What Kate Wore noted this is particularly unusual for Kate as she tends to only wear three rings stacked on her left ring finger: her engagement ring, wedding ring and eternity ring.
While the Queen, 93, wore what is believed to be an updated version of an emerald necklace - the Greville Emerald Necklace.
Prince Charles and the Camilla, the Duchess of Cornwall, were also in attendance.
But Prince Harry and Meghan Markle were noticeably absent from the reception.