Catherine wore Diamond and Pearl Leaf Brooch on loan from Her Majesty in 2017 when she visited Belgium to Mark the Centenary of Passchendaele. The brooch features 3 pearls set in the center of a paved leaf. Duchess again wore the brooch at the annual festival of Remembrance in November 2018.
The brooch does not seem to have any long history. It was first seen in 1999, when Queen Elizabeth II wore it during her South Korea visit. After that the brooch was worn by Duchess of Cambridge in 2017.