I found this story on the web:
"...Spanish king would sully the opal's already sordid reputation further still. In the late 19th Century, Alfonzo XII fell madly in love with a beautiful aristocrat named the Comtesse de Castiglione. The Comtesse reciprocated the King's affection, but months before the pair were to wed the faithless Alfonzo married another woman, the Princess Mercedes. Vowing to get even, the Comtesse sent the couple a wedding present in the form of a magnificent opal set in a huge ring of the purest gold. The princess was immediately smitten by the gift and insisted that her husband slip it on her finger. He obliged, and two months later the princess mysteriously died.
After the funeral Alfonzo gave the ring to his grandmother, Queen Christina, who almost immediately thereafter also expired. After that the ring passed to Alfonzo's sister, the Infanta Maria del Pilar. Maria died as well, apparently victim to the same weird illness that had taken the other two women. The ring was up for grabs yet again, and when Alfonzo's sister-in-law expressed an interest, he let her have it with the usual result.
Deeply depressed by then, the King decided to end it all by slipping the ring on his own finger, just as Cleopatra had embraced the asp to terminate her own misery. In little over a month, the ring did to Alfonzo what the snake had done to the Egyptian Queen. The ring was finally attached to a gold chain and strung around the neck of a statue of the patron saint of Madrid, the Virgin of Alumdena. That put an end to the incredible chain of tragic circumstances..."
