Isabel of Portugal: Duchess of Burgundy, Queen of Italy, Naples, the Germans, and Spain, Empress of the Holy Roman Empire

Isabel of Portugal, regent of Spain (born 24 October 1503)

Isabel of Portugal was the daughter of Manuel I of Portugal and his second queen, Maria of Aragon, who was the daughter of Isabella of Castile and Ferdinand of Aragon. 

Isabel of Portugal in 1526,
at the time of her marriage

(Interestingly, Maria was the second of Isabella and Ferdinand's daughters to marry Manuel--Maria's elder sister, Isabel, had been married, first, to Afonso of Portugal, but after his untimely death just a year after their marriage, the young widow was married, much against her wishes, to Manuel, who was Afonso's uncle. And, by the way, after Maria of Aragon's death,  Manuel married his niece, Eleanor of Austria . . . So, yay for traditional marriage, I guess.)

Named after both her grandmother and her aunt, Isabel of Portugal was married to her cousin, the Holy Roman emperor Charles V, in 1526. (According to the terms of the marriage arrangement, Isabel's brother, John III of Portugal, married Charles's sister, Catherine of Spain, a woman whom we have met before.)

Through her marriage, Isabel gained a number of titles, some of them indicated in the heading of this post. She was the Holy Roman empress, the queen of the Germans, the queen of Italy, the queen of Spain, the queen of Naples and Sicily, and duchess of Burgundy. But she also gained another title: regent of Spain.

Charles recognized the importance of marrying a woman with the ability to govern. In a letter to his brother, he noted that marrying Isabel of Portugal was "the only sure way of securing stability in the Spanish kingdoms in his absence." 

When Charles was forced to leave Spain for the empire, he appointed his wife as his regent, a role she fulfilled admirably. The Cortes recognized her position on 27 July 1527; she served as regent from 1529 until 1532.  She was personally involved, as well, in the education of her two children, Philip, born in May 1527, and Mary, born in 1528. Charles returned to Spain in April 1533, and when he left again in April 1535, Isabel was regent once more. 

But after Isabel's early death in 1539, at the age of thirty-six (she died after giving birth to a child, her sixth, a stillbirth), Charles had difficulty in finding a suitable replacement for her. Historian Andrew Wheatcroft describes the emperor as "hamstrung" because he "could find no one to replace her effectively." He would not "countenance the appointment of any of his male kin whom he judged inadequate to the role," nor any female "unless she was married, widowed, or old enough to be widowed."

A portrait by Titan, from 1548,
after Isabel's death

Ultimately Isabel's eldest son, Philip II, was old enough to act his father's behalf; Charles appointed him to act as his representative in Spain in 1543. 

In the same year, Philip married his first cousin Maria Manuela of Portugal, the eldest daughter of John III of Portugal (Philip's maternal uncle) and Catherine of Spain (his paternal aunt). By 1545, Maria had given birth to a son and heir, Carlos, and had died. In 1554, when Philip left Spain for his second marriage, this one to Mary Tudor, queen of England, he turned to his sister Joanna of Castile to act as regent of Spain in his place.

There is no biography of Isabel of Portugal. You can find references to her in biographies of Charles V and of her son, Philip, but I like Andrew Wheatcroft's The Habsburgs: Embodying Empire, quoted here, because he focuses quite deliberately on the Habsburg strategy of using female family members as regents.