Peter of Castile in the context of "Black Prince's Ruby"

The Alcázar of Seville, officially called Royal Alcázar of Seville (Spanish: Real Alcázar de Sevilla or Reales Alcázares de Sevilla), is a historic royal palace in Seville, Spain and one of the official residences of the Spanish royal family. It was formerly the site of the Islamic-era citadel of the city, begun in the 10th century under the Umayyads and then developed into a larger palace complex by the Abbadid dynasty (11th century) and the Almohads (12th to early 13th centuries). After the Castilian conquest of the city in 1248, the site was progressively rebuilt and replaced by new palaces and gardens. Among the most important of these is a richly decorated Mudéjar-style palace built by Pedro I during the 1360s.

The palace is a preeminent example of Mudéjar style in the Iberian Peninsula and also includes sections with Gothic and Renaissance elements. The upper storeys of the Alcázar are still occupied by the royal family when they visit Seville and are administered by the Patrimonio Nacional. It was registered in 1987 by UNESCO as a World Heritage Site, along with the adjoining Seville Cathedral and the General Archive of the Indies.

The Caroline War was the second phase of the Hundred Years' War between France and England, following the Edwardian War. It was so-named after Charles V of France, who resumed the war nine years after the Treaty of Brétigny (signed 1360). In this part of the conflict, the Crown of Castile emerges as a supporter of France. The Kingdom of France dominated this phase of the war.

The Black Prince, eldest son and heir of Edward III of England, spent a huge sum of money in order to restore Peter the Cruel to the throne of Castile. The Castilian King was unable to repay him, however, so the Black Prince raised taxes in his domains in Aquitaine. The people's complaints were unheeded, so they appealed to the French King Charles V. In May 1369, the Black Prince received summons from the French king demanding his presence in Paris. The prince refused, and Charles responded by declaring war. He immediately set out to reverse the territorial losses imposed at Brétigny and he was largely successful in his lifetime. His successor, Charles VI, made peace with the son of the Black Prince, Richard II, in 1389. This truce was extended many times until the war was resumed in 1415.

Henry II (13 January 1334 – 29 May 1379), called Henry of Trastámara or the Fratricidal (el Fratricida), was the first King of Castile and León from the House of Trastámara. He became king in 1369 by defeating his half-brother Peter the Cruel, after numerous rebellions and battles. As king he was involved in the Fernandine Wars and the Hundred Years' War.

The House of Burgundy, also known as the Castilian House of Ivrea, is a cadet branch of the House of Ivrea descended from Raymond of Burgundy. Raymond married Urraca, the eldest legitimate daughter of Alfonso VI of León and Castile of the House of Jiménez. Two years after Raymond's death, Urraca succeeded her father and became queen of Castile and León; Urraca's and Raymond's offspring in the legitimate line ruled the kingdom from 1126 until the death of Peter of Castile in 1369, while their descendants in an illegitimate line, the House of Trastámara, would rule Castile and Aragón into the 16th century.

Catherine of Lancaster (Castilian: Catalina; 31 March 1373 – 2 June 1418) was Queen of Castile by marriage to King Henry III of Castile. She governed Castile as regent from 1406 until 1418 during the minority of her son.

Queen Catherine was the daughter of John of Gaunt, 1st Duke of Lancaster, and his second wife, Constance of Castile (the eldest daughter and heiress of King Peter of Castile, who died at the hands of his half-brother Henry II). She was born in Hertford Castle, her father's chief country home, on 31 March 1373. Catherine became Queen of Castile through her marriage to Henry III.