From a cushion-cut jewel to Princess Diana's famous sapphire, here's everything to know about these well-known sparklers.

The most expensive royal engagement ring belongs to Grace Kelly, the Hollywood actress who became Princess of Monaco. Kelly’s Cartier ring was given to her by Prince Rainier III in 1956.

This was especially the case for then-Prince Charles in 1981 when he revealed that he had proposed to Princess Diana with a 12-carat sapphire ring. The jewel soon became one of the world’s most ...