"Set with diamonds, sapphires, rubies and emeralds, the bejewelled piece features the cypher of her father, King George VI," Zack Stone, a fine jewelry expert from U.K. retailer Steven Stone, shared with WWD.

Middleton — who announced in January that she is in remission from cancer — was spotted conversing and laughing with her kids, as they made their way to Buckingham Palace. The matriarch sweetly matched her young daughter for the event in aquamarine outfits.