In 1953, the rough gem was cut and polished to a weight of 23.6 carats and used to make a brooch by Cartier.

It was placed alongside 203 white diamonds, including brilliants, marquises, and baguettes, before it was given back to Her Majesty.

The Queen has worn the brooch for notable royal occasions over the years, including the 1981 weeding of Prince Charles and Princess Diana, as well as the wedding of Prince Edward and Sophie, the Duchess of Wessex in 1999.

More recently, Elizabeth wore the brooch to the Royal Ascot in 2011 and to the Elysée Palace during an official visit to Paris in 2014.