There it right in front of the Crown of England. It has quite the story.
The Black Prince's Ruby enters the "stage of history" in middle of the 14th century as the possession of Abū Sa'īd, the Moorish Prince of Granada. At that time, the rule of Castile was being centralized to Seville and the Moorish Kingdom of Granada was being systematically attacked and reverted to Castilian rule as a part of the Christian Reconquest of the Iberian peninsula. Abū Sa'īd in particular was confronted by the belligerency of nascent Castile under the rule of Peter of Castile, also known to history as Don Pedro the Cruel. According to historical accounts, Abū Sa'īd wished to surrender to Don Pedro, but the conditions he offered were unclear. What is clear is that Don Pedro welcomed his coming to Seville. It is recorded that he greatly desired Abū Sa'īd's wealth. When Abū Sa'īd met with Don Pedro, the don had Abū Saī'd's servants killed and may have personally stabbed Sa'īd to death himself. Upon searching Sa'īd's corpse, the spinel was found and added to Don Pedro's possessions.
In 1366, Don Pedro's illegitimate brother, Henry of Trastámara, led a revolt against Don Pedro. Lacking the power to put down the revolt unaided, Don Pedro made an alliance with the Black Prince, the son of Edward III of England. The revolt was successfully put down and the Black Prince demanded the ruby in exchange for the services he had rendered. While historians speculate that this was contrary to Don Pedro's desires, he had just suffered a costly civil war and was in no position to decline. It can be assumed that The Black Prince took the Ruby back to England, although it is absent from historical records until 1415.
Edward of Woodstock KG (15 June 1330 – 8 June 1376), called the Black Prince, was the eldest son of King Edward III and Philippa of Hainault, and the father of King Richard II of England. He was the first Duke of Cornwall (from 1337), the Prince of Wales (from 1343) and the Prince of Aquitaine (1362–72).
He was called "Edward of Woodstock" in his early life, after his birthplace, and since the 16th century has been popularly known as the Black Prince. He was an exceptional military leader, and his victories over the French at the Battles of Crécy and Poitiers made him very popular during his lifetime. In 1348 he became the first Knight of the Garter, of whose order he was one of the founders.
During his campaign in France, Henry V of England wore a gem-encrusted helmet that included the Black Prince's Ruby. In the Battle of Agincourt on October 25, 1415, the French Duke of Alençon struck Henry on the head with a battleaxe, and Henry nearly lost the helmet, along with his life. However, the Battle of Agincourt was won by Henry's forces, Henry did not die, and the helmet was preserved along with the Black Prince's Ruby. Richard III is reported to have also worn the Black Prince's Ruby in his helmet at the Battle of Bosworth Field where he died.
James I had the Black Prince's Ruby set into the state crown near the turn of the 17th century, where it remained until the time of Oliver Cromwell. With the exception of The Coronation Chair, and several other minor items, Cromwell had the principal symbols of the king's power within the Crown Jewels disassembled and sold, having the metal melted down and made into coins. A British jeweller bought the Black Prince's Ruby in the days of the Commonwealth, but sold it back to the crown (Charles II) when the monarchy was restored in 1660. At the Coronation of Queen Victoria in 1838 she was crowned with a new Imperial State Crown made for her by the Crown Jewellers Rundell and Bridge, with 3093 gems, including the ruby at the front. This was then remade in 1937 into the current, lighter, crown.
And there is sits to this day.