6. Sarah Ferguson
Remember when we said that Princess Eugenie's ring closely resembled her mother's? Well, we weren't kidding, were we? 

Here we see Sarah Ferguson's ring, given to her by Prince Andrew in 1986. Made by Garrad, it has an oval-cut Burmese ruby surrounded by 10 diamonds set on a yellow gold band. Apparently, Prince Andrew chose a ruby because it reminded him of Sarah's red hair. Though the two married in 1986, they separated in 1992 and divorced four years later.