The Duchess of Cambridge's engagement ring, which belonged to Prince William's late mother Princess Diana, was valued at £28,000 when Prince Charles proposed to her with it. Now valued at £300,000   It has 14 solitaire diamonds surrounding a 12-carat oval blue Ceylon sapphire, set in white gold. Kate Middleton Engagement Ring, Princess Diana Engagement Ring, Non Diamond Engagement Rings, Colored Engagement Rings, Celebrity Engagement Rings, Engagement Rings Sapphire, Wedding Rings Engagement, Middleton Wedding, Middleton Style