Isabella of Portugal (; 24 October 1503 – 1 May 1539) was the empress consort of her cousin Charles V, Holy Roman Emperor, King of Spain, Archduke of Austria, and Duke of Burgundy. She was Queen of Spain and Germany, and Lady of the Netherlands from 10 March 1526 until her death in 1539, and became Holy Roman Empress and Queen of Italy in February 1530. She was the regent of Spain because of her husband's constant travels through Europe, focusing on the kingdom's policies independent of the Empire and managing the economy.
Childhood
Isabella was born in Lisbon on 24 October 1503 and named after her maternal grandmother (Isabella I) as well as her maternal aunt, who had been her father's first wife. She was the second child and first daughter of King Manuel I of Portugal and his second wife, Maria of Aragon. Isabella was second-in-line to the throne until the birth of her brother Luis in 1506.
Isabella was educated under the supervision of her governess Elvira de Mendoza. Her studies included mathematics, Renaissance classics, the languages of Latin, Spanish and French besides her native Portuguese, etiquette, and Christian doctrine. Isabella and her siblings were punished by their mother, "when they deserved it, without pardoning any of them". At the age of 14, her mother died. She and her sister Beatrice inherited her properties, plus the income from Viseu and Torres Vedras.
Engagement and marriage
As the eldest daughter of Manuel the Fortunate, Isabella was a rather attractive candidate for marriage. The ideal candidate for her husband was her first cousin Charles, son of Maria's sister, Joanna I of Castile and her husband Philip, Duke of Burgundy. Their marriage would bring a strong alliance between Spain and Portugal, in accordance with the wishes of their grandparents, Isabella I of Castille and Ferdinand II of Aragón. It would also facilitate the continued exploration of the oceans without incurring clashes, as Portugal was the only naval power that could challenge Spain's supremacy in the Atlantic Ocean. Plus, as Charles was sovereign of multiple kingdoms, it was necessary that Portugal, Christendom's richest kingdom, would fall under Spain's orbit and not of France, which had happened in the War of Castilian Succession. Moreover, because he had been raised in Burgundy, the Spanish nobles and subjects reportedly insisted that he should marry a princess from the Iberian peninsula.
However, the 18-year-old Charles was in no hurry to marry and instead sent his sister Eleanor to marry Isabella's widowed father in 1518. Charles's Flemish advisors, especially William de Croÿ, later convinced him to relegate the Portuguese alliance to the background and replace it with an alliance with England. In 1521, Charles became engaged to his other first cousin, Mary Tudor, daughter of Henry VIII and Catherine of Aragon, who was 16 years younger than Charles and still a child. Their engagement sought to undo an alliance between England and France articulated by the ambitious Cardinal Thomas Wolsey. Many in Portugal took their Infanta's rejection as an offense, but Isabella remained determined she would marry her powerful cousin or enter a convent. By 1525, Charles was no longer interested in an alliance with England and could wait no longer for Mary to get older because he was determined to have legitimate children. His engagement was called off, the alliance with England was abandoned, and he finally sought to marry Isabella. There were many more advantages – she was closer to him in age (she was only 3 years his junior), fluent in Spanish, and offered a dowry of 900,000 Portuguese cruzados (or Castilian folds), which was more than enough to solve many of his financial problems brought on by the Italian War of 1521–26.
Charles wasted no time in securing a papal dispensation for first cousins and the marriage contract for an alliance with Portugal was made - Isabella would marry him and her brother, King John III of Portugal, would marry Charles' youngest sister, Catherine of Austria. Charles intended to wed and then leave his future wife as regent to govern Spain while he went to Central Europe to deal with political and religious troubles there. In January 1526, Isabella traveled to Spain. Upon her arrival, she met the Duke of Calabria, the Archbishop of Toledo and the Duke of Béjar at the Spanish-Portuguese border. They escorted her to Seville, where she would wait a week for Charles. In the end, their wedding took place the very next day just after midnight on 11 March in the Palace of Alcázar of Seville.