Why is up for auction, when the royal family should keep it? And if it isn't owned by the royal family, shouldn't they try to buy it back?
It probably was inherited out of the senior family line and into the cadet branches, who eventually sold it. It came into the Swedish royal family the same way: it passed from the Leuchtenberg ruling family to the Swedish royal family through Queen Josephine, when she married, instead of becoming part of the Prince's inheritance. A lot of important jewelry moved around Europe as part of a princess's trousseau (after all, she couldn't arrive at her new court without jewelry or with all new jewelry, like a parvenu). Today, most royal families have their own rule about what jewelry must stay with the main family line and what can be given at the owner's discretion.
In this necklace's case, it was inherited by the second son, who became Oscar II of Sweden (1829-1907), and then by Count Oscar Bernadotte (1859-1953). Count Oscar married a lady-in-waiting and was disinherited from the royal family at this point. Moving forward, there are pictures of Countess Gerty Bernadotte, his daughter in law, wearing it in what seems to be the mid 20th century. From there, I am not sure what happened but it was part of the collection of Mauboussin, the jeweller, when it was auctioned off by Christie's in 1995. I imagine the family ran into financial troubles and quietly sold off jewelry to raise funds. It would hardly be the first time that a noble family did a private sale to a jeweler, to avoid gossip and raise money at the same time.
I doubt the royal family would try to buy it back. First, the Bernadottes have an enviable (by royal standards) jewelry collection, well protected in the family fund. It is large enough to outfit the queen, her daughters and several of the older generation as well. Second, in today's economy, spending several million dollars to buy jewelry would not be a popular move. Finally, this piece does not have such a strong connection to the family or the country. It is a foreign piece only worn by two queens.
