|Photos (clockwise from top left): Queen Mary of the United Kingdom; tiara detail; Princess Marina, Duchess of Kent; the Duchess of Kent; Princess Marina, Duchess of Kent|
One Cambridge tiara that will sadly not be available for Kate or her daughters to wear is this one, the originally tiara from the Cambridge family sapphire parure. As is the case with most Cambridge tiaras, this piece's ownership chain traces back to Augusta of Hesse-Kassel, the wife of George III's son, Prince Adolphus, the Duke of Cambridge. It was a part of a sapphire parure that also included a necklace, a stomacher, and brooches.
Augusta left the parure, including the tiara, to her daughter, Princess Augusta Caroline, who had married the Grand Duke of Mecklenburg-Strelitz in 1843. (Here's a link to a miniature of Augusta Caroline wearing the tiara, painted in 1861.) Augusta Caroline lived an impressively long life, and she maintained her connections to the British royal family throughout. When she died in 1916, she left the Cambridge sapphires to her niece, Queen Mary.
Queen Mary could never resist tinkering with her jewels, so it should perhaps come as no surprise that she augmented and altered the parure after inheriting it from her aunt. Mary took the original necklace from the parure and had it transformed into brooches and earrings. She replaced the necklace with a sapphire collier that she already owned, and she added two bracelets to make the parure even more complete.
Mary selected the Cambridge sapphires in 1935 as her wedding gift to her new daughter-in-law, Princess Marina of Greece and Denmark. Marina married the Duke of Kent, and some of the sapphires have stayed in the family ever since -- you'll sometimes see them called the Kent sapphires for this reason. Marina innovated with the jewels in the parure just as her mother-in-law had, creating a second button tiara using elements from the necklace, and modifying the bracelets so they could be worn as pieces to lengthen the original tiara.
When Marina died, the sapphire parure was left to her daughter-in-law, the current Duchess of Kent. But here's where the trouble starts: the Kents decided at some point to dispose of certain parts of the parure, selling the original tiara, the stomacher, and the necklace. The family apparently retains the remaining parts of the parure, although it's possible that one of the bracelets was also sold. So the parure still technically has a tiara -- the new button tiara created for Princess Marina -- but the whereabouts of Augusta's original sapphire tiara are unknown today.
Some live in hope that the buyer of these heirlooms was another member of the royal family, maybe even the current queen. But that's all conjecture at this point. The pieces have not appeared in public in any venue since the sale. Best case scenario -- the original tiara is maybe hidden away today in the BP vaults? Who knows?