Kate Middleton attended the Commonwealth Day service while sporting Princess Diana's brooch.

The Queen Alexandra Three Feathers Brooch has a price tag of $680,000.

Kate wore the brooch without the traditional cabochon-drop emerald attachment.

Princess Alexandra of Denmark received the brooch as a present in 1863.

Prince Charles urged nations to collaborate for the benefit of humanity.

Climate change, biodiversity loss, and economic cooperation are all global issues that the Commonwealth can help to resolve.

There are 1.5 billion people under 30 in the Commonwealth, and their culture and history are very different.

Problems can be solved by listening to one another.

Experts and fans were divided about Kate's jewelry choice.