It is thought that at some point he gave the diamond to his son, Joseph Francis (1895-1957). Minutes taken on June 1st, 1933 record that the diamond, at the time belonging to Archduke Joseph, was at the time deposited with the Hungarian General Credit Bank in the presence of a state counsellor. Three years later the diamond was sold to a European banker who kept it in a safe deposit box in France during World War II, where it fortunately escaped the attention of the Nazis.The location of this stone remained a mystery until it came up for auction in London in June, 1961. At the time it was believed to be the largest loose fine quality diamond ever to have been auctioned in Great Britain, but it was withdrawn from the sale when the bidding stopped at £145,000.Later it was reported that a syndicate of Hatton Garden buyers had made an unsuccessful bid for the diamond. It came up for sale again at Christie’s in Geneva in November of 1993, when it was sold for $6,487,945. The diamond originally weighed 78.54 carat but was slightly recut in the late-1990’s by Molina Fine Jewelers (the diamond’s present owners) down to its current 76.45 carat weight.

The diamond has been graded as being Internally Flawless.

 

UPDATE
Christie’s Geneva will auction the legendary Archduke Joseph Diamond on November 13. This 76.02-carat, D, IF Golconda diamond is the top lot of the fall jewelry auction season for Christie’s. The Archduke Joseph Diamond is expected to achieve ”in the region of $15 million to $25 million,” according to the auction house.

François Curiel, the international head of Christie’s jewelry department, said, ”The magic of auction sometimes brings back great gems to our sales rooms more than once.

”The Archduke Joseph Diamond created a sensation when Christie’s Geneva offered it for sale the first time in November 1993 where it realized $6.5 million – the equivalent of $10.5 million today,” Curiel said.

”This November we have the privilege to give both new and established collectors the opportunity to own a piece of history once again,” he said.

Sources:
Wikipedia
Famous Diamonds
Famous, Notable and Unique
RapNet