E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Pitt Diamond or The Regent.
Called Pitt diamond because it once belonged to Mr. Pitt, grandfather of the famous Earl of Chatham. Called the Regent diamond from the Duke of Orleans, Regent of France, who purchased it. This famous diamond was worn in the sword-hilt of Napoleon, and now belongs to the King of Prussia.