Four generations have worn the Cartier Halo tiara, originally owned by the Queen Mother and most recently taken out for a spin by the Duchess of Cambridge on her wedding day. The crown was made by Jacques Cartier 75 years ago, and is emblematic of a long, shimmering history between the French jeweler and the British royal family, now the subject of a two-part webinar. Representing the former is Francesca Cartier Brickell, the great-granddaughter of Jacques and author of The Cartiers. Representing the royal family is Caroline de Guitat, deputy surveyor of the Queen’s Works of Art. Part II kicks off with a piece that changed the course of history, one of two stones cut from an emerald the size of a bird’s egg: Wallis Simpson’s engagement ring. —J.V.