Kate Middleton wore a brooch that previously belonged to Princess Diana at the Commonwealth Day service.

The brooch is the Queen Alexandra Three Feathers Brooch, which has been passed down through several generations and is valued at $680,000.

Kate wore the brooch without the cabochon drop emerald which is usually attached.

The brooch was gifted to Princess Alexandra of Denmark in 1863.

Prince Charles encouraged nations to "strive together" for a "global common good" on Commonwealth Day.

Climate change and the loss of biodiversity and economic cooperation are all important global problems that the Commonwealth can help solve.

The Commonwealth boasts a rich range of philosophy, culture, history, and experience with 1.5 billion individuals under 30.

By listening to each other, solutions to many of the problems faced by the Commonwealth can be found.

Kate's nod to Princess Diana through her choice of jewelry sparked conversations among experts and fans.