Kate's engagement ring first belonged to her late mother-in-law, the iconic Diana, Princess of Wales. When then Lady Diana Spencer became engaged to Prince Charles in 1981, she was presented with a tray of rings and stones by the Crown Jeweler at the time, Garrard. The stone is blue, 12 caret sapphire surrounded by 14 diamonds in an 18-karet white-gold setting. In 1981 it cost £28,000. Prince William carried it in a rucksack for weeks while the pair holidayed in Kenya before presenting it to Kate while they stayed at a mountain cabin. The ring was too large on Kate, but rather than have the ring resized by reshaping it, she had two raised studs placed on the inside of the band. Note that G. Collins & Sons undertook this resizing, as they replaced Garrard as the Crown Jeweler in 2007.
Sapphire Engagement Ring