John I of Castile : biography
To secure the succession of the throne of Portugal, the Portuguese Cortes covenanted marriage between Beatrice and John I of Castile, on 2 April 1383 in Salvaterra de Magos, with the stipulation that upon the death of Ferdinand I, with no issue of sons, the crown would pass to Beatrice, and her husband become titular king of Portugal. Although John I of Castile could call himself king of Portugal, the Spanish and Portuguese parties agreed not to unite the kingdoms of Castile and Portugal, and therefore, Leonor, widow of King Ferdinand, would remain regent of the government of Portugal till Beatrice had a son who reached fourteen years of age, who would assume the title and office of King of Portugal, and his parents’ claim cease. If Beatrice died childless, the crown would pass to other hypothetical younger sisters, and if not, the crown would pass to John I of Castile, and through him to his son Henry, thus disinheriting the line of Inês de Castro. Pedro de Luna, a Papal legate to the realms of Castile, Aragon, Portugal and Navarre, pronounced the betrothal in Elvas on 14 May, and the wedding ceremony took place on 17 May at the Cathedral of Badajoz. To ensure compliance with the treaty, on 21 May a group of Castilian knights and prelates of the kingdom swore an oath to depose their king if the Castilian king dishonoured the commitments agreed in the treaty, and a corresponding group of Portuguese knights and prelates vowed to do the same if the king of Portugal broke the treaty with Castile, among them the Master of Aviz.
John I of Castile assumed the title and coat of arms of King of Portugal, which investiture was recognized by the Pope of Avignon, and ordered the deployment of his troops when the Bishop of Guarda and chancellor to Beatrice, Afonso Correia, promised to deliver the support of the people. He then entered the country with his wife to ensure the obedience of the Portuguese people to him as King by the right of his wife, although they considered him merely a pretender.
For John I of Castile, his marriage to Beatrice was supposed to maintain a protectorate over the Portuguese territory and prevent the English from invading the peninsula. However, the expectation of a Spanish commercial monopoly, fear of Castilian rule and the loss of Portuguese independence, reinforced by popular opposition to the regent and her allies, led to an uprising in Lisbon in late November and early December. The loss of independence was unthinkable for the majority of the people. The Master of Aviz, future John I of Portugal, ignited the rebellion on 6 December 1383 when he broke into the royal palace and assassinated Leonor’s lover, Conde Andeiro, after which the common people rose up against the government at the instigation of Alvaro Pais. Bishop Martinho, under suspicion of conspiring with the enemy, was defenestrated by the citizens when Lisbon was besieged by the Castilians in 1383. The uprising spread to the provinces, taking the lives of the abbess of the Benedictine nuns in Évora, the Prior of the Collegiate Church of Guimarães, and Lançarote Pessanha, Admiral of Portugal, who was murdered at the Castle of Beja. The rebellion was supported by the bourgeoisie but not by the aristocracy. Queen Leonor fled with the court of Lisbon and took refuge in Alenquer, the property of the queens of Portugal. She appealed to John I of Castile for help.
In Lisbon, Alvaro Pais proposed that he and Leonor marry and hold the regency together, but Leonor declined; upon the news of the coming of the Castilian king, the Master of Aviz was elected Regent and Defender of the Realm on 16 December 1383, as an advocate for the rights of the queen’s son, the Infante Juan. João das Regras was appointed as chancellor and Nuno Álvares Pereira as constable, and requested England to intervene. The Master of Aviz tried to besiege Leonor at Alenquer but fled to Santarém to prepare the defense of Lisbon. In Santarém, Leonor proceeded to raise an army and sought help from John I of Castile, who decided to take command of the situation in Portugal, and left a Regency Council consisting of the Marquis of Villena, the Archbishop of Toledo and the Steward of the King to rule Castile in his absence. In January 1384 he began the journey to Santarém with Beatrice to answer the call of the Queen Regent to restore order in Portugal. On 13 January King John I and Queen Beatrice obtained the waiver of the rule and the government in their favour, which caused many knights and castle lords to submit and swear allegiance to the royal couple. Since Leonor had conspired against John the Infante, she was sent to the monastery of Tordesillas. This served the purposes of the Master of Aviz to justify his leading the revolt; he had violated the oath he swore at the Treaty of Salvaterra de Magos.