Kate Middleton doesn't always wear the sapphire and diamond engagement ring that was once worn by her late mother-in-law Princess Diana, and there is a standout reason why.

a ruby and diamond ring by Van Cleef & Arpels, sold at auction in 2011 for $4,226,500. Here Is Elizabeth Taylor's 16-Carat Sapphire Engagement Ring From Victor Luna? A year after splitting from ...

The ring in question: a 5-carat black diamond by Itay ... and market for coloured stone engagement rings has grown as knowledge and information about coloured stones – besides the obvious big players ...