Prince Georg Friedrich, 36, great-great-grandson of the last German Kaiser, inherited the nearly 35 carat diamond as part of the estate of the House of Prussia, after it was worn by some of Europe's most important queens over the previous four centuries.
“I have had the stone in my hands, it is beautiful, amazing,” Philipp Herzog von Württemberg, chairman of Sotheby's Europe, told The Local.
Sotheby's is auctioning the diamond in May in Geneva, where the estimated price has been set between $2 million and $4 million. The 34.98 carat diamond measures 22.78mm tall, 19.58mm wide and 10.98mm deep.
“It is set very simply in a hoop with a ring so it could be put on a necklace. It is a beautiful stone, but what is at least as exciting is the history it carries, with previous owners including the Medicis, Queen Mary and all the kaisers of Prussia.”
He said no information was being released over the reasons behind the sale.
“It is the most important and oldest stone to come onto the art market,” said Württemberg. He said a similarly sized but much more modern diamond sold from the estate of Liz Taylor, had an estimated price of between $2.5 million and $3.5 million and it sold for $8 million.
“With this one, the price which any buyer will pay will depend on their appreciation of the history behind it. I think it will sell for many more times the estimated price.”
Bought in Constantinople
The Beau Sancy was bought some time in the mid to late 1500s by Nicolas de Harlay, Lord of Sancy, in Constantinople, and is thought to have come from the mines of south-central India near the city of Golconda, according to Sotheby's. Other famous diamonds such as the Hope, the Koh-i-Nor and the Regent came from that area.
The diamond passed through many of the major European royal houses. It was bought in 1604 by Henri IV of France, who gave it to his wife Marie de Medici. She had the stone mounted at the top of the crown she wore at her coronation in 1610 – featured in a portrait by Frans II Pourbus the Younger, which hangs in the Louvre.
After Henri IV was assassinated, she was exiled from France and fled to the Netherlands where she was forced to sell many of her possessions, including her treasured diamond. The Beau Sancy was bought in 1641 by Prince Frederick Hendrick of Orange-Nassau for 80,000 florins – the most important expenditure of that year's state budget.
It was then used to seal the arrangement of the wedding between Frederick Hendrick's son Willem to Mary Stuart, herself actually the granddaughter of Marie de Medici. When Mary Stuart was widowed she headed for England to support her brother Charles II in his struggle for the English throne.
After the diamond was pawned to settle her debts, it re-entered the treasure of the House of Orange-Nassau in 1677 when Willem III married Mary II Stuart, daughter of King James II of England.
English crown jewels
When the couple became rulers of England, the Beau Sancy joined the collection of the Queen of England. It did not stay there long though, reverting to the House of Orange-Nassau when Willem and Mary died childless.
After a dispute between heirs to the house of Orange, Friedrich I who was crowned first King of Prussia in 1701, swapped all his inherited jewels for the Beau Sancy – and made it the prime ornament of the new royal crown of Prussia.
There it remained, the biggest gem in the Prussian collection, worn by the women of the family on important occasions and by every royal bride until the dissolution of the monarchy.
It stayed in Germany even when the last German emperor and king of Prussia fled to exile in Holland in November 1918. By the end of World War II the crown jewels were hidden in a bricked-up crypt in Bückeburg where it was later found by British soldiers – and returned to the House of Prussia where it has remained - until May.
It has only been put on public display four times over the last 50 years – in 1972 in Helsinki, in 1985 in Hamburg, in 2001 in Paris and in 2004 in Munich.
Württemberg said he hoped the diamond would remain in Europe, although he admitted there was no way to guarantee this. “Perhaps the French state could buy it – the Louvre museum has the partner stone [the Grand Sancy] which was originally bought with this one. That would bring them together.
“But there are also many newly-rich potential buyers who might place great importance on the history of this stone.”
The Beau Sancy will be taken on a tour of the major auction centres across the globe during April and into early May, before the auction in Geneva on May 15.