The famous diamond belonging to Louis XIV
The French Blue is a blue diamond that belonged to Louis XIV. It is estimated to weigh 69 carats.
It is said to have been brought back from India in 1668, then cut by order of the king in 1673, by the crown jeweller, Jean Pitau. It was stolen along with many other jewels (including the Sancy and the Regent) in 1792 during the burglary of the Hôtel du Garde Meuble.
However, the recently discovered lead model suggest that the French Blue was the origin of the Hope that appeared twenty years later in England. Even today, it is still the largest blue diamond ever discovered.