The Black Prince's Ruby

The Castille (a medieval kingdom from the Iberian Peninsula) was ruled by a terrible and justifiably named king in  the fourteenth century.  One day, Abu Said who was an Arab cheiftain who still ruled Spain came to surrender. After hearing that Abu Said had with him jewels of great worth, including a exquisite ruby, in which Peter welcomed him amiably and invited the chieftain to dinner.  During the banquet Peter had Abu's servants killed while he personally stabbed Abu to death. The infamous ruby was found on the corpse.

Peter called England to his aid when his subjects and his brother rebelled against him. Peter was also called the Black Prince. In return of England's aid, Peter rewarded them with Abu Said's ruby.  The ruby was made into a part of the Crown Jewels of England and was worn by Henry V on his helmet in 1415 when he crushed the French forces at Agincourt.  Later at the Battle of Bosworth, Richard III wore the ruby in his helmet.  Under Oliver Cromwell the Puritans destroyed, dispersed, and melted the Crown Jewels. The Black Prince's Ruby was bought by a jeweler who resold to Charles II after the reformation of the Stuarts in 1660.

Interesting enough, later testing of the ruby found it to be not a ruby but a precious spinel, which is a natural stone.  This spinel  has almost the same value as a ruby and is very distinctive in shape and size.