If diamonds are a girl’s best friend, the Wittelsbach would make one heck of a BFF. The 35.56-carat blue diamond dates back to the 17th century, when King Philip IV of Spain selected the jewel to be part of his daughter’s dowry. The diamond passed among Austrian and Bavarian royalty for centuries, but after World War I Bavaria became a republic and the jewel was repossessed by the state. Christie’s auction house tried to sell it in 1931 but apparently found no buyers. The diamond disappeared for a few decades only to resurface in 1962. A private collector purchased it in 1964, but sold it in 2008 for $23.4 million.