It isn't the smartest thing to marry a prince that is nicknamed "the Fair" when you have a tendency to jealousy, one would say. But princesses in the 15th century couldn't choose their husbands; their marriages were arranged for political reasons. Joan was one of the luckier girls, since she was betrothed to a man she absolutely adored: Philip of Austria. He lived up to his nickname, and on the night the two first met, it was love - or lust - at first sight. Philip insisted they would marry immediately so the young couple could love each other passionately.
Unfortunately, their attraction would turn out to be fairly unequal: Philip's feelings for Joan were mere desire, whereas Joan loved her husband obsessively. But he was young, handsome and on top of that he was a monarch (he ruled the Low Countries from the age of 18), so women lay to his feet and he loved it. He acted as if he was a young bachelor, drinking, feasting and having sex excessively. Joan was extremely jealous; she wanted her husband for her and herself only.
She often was moody and depressed, or could also break out in jealous rages. Philip couldn't care much, he would rather make things worse by avoiding her bedroom after they had been fighting over one of his excesses. She would cry of anger and despair and bump to the wall ceaselessly. Instead of starting to hate him, however, her mad love for him remained. He was all that she cared for: she lost all interest in politics and became isolated at court.
Between 1497 and 1500, both her older siblings died, making her the heiress of the united provinces of Spain including the overseas territories. The couple, that had been living in Flanders up until that moment, returned to Spain. They were welcomed with open arms by Joan's father Ferdinand II, but her mother Isabella encountered them with chilling coldness, worsening Joan's nervousness. Philip couldn't get used to the Spanish court life with its endless religious services and no possibility to enjoy women. He returned to Flanders in 1502, leaving Joan behind without a word of goodbye. When she find out, she just wanted to ride after him and drag him out of the arms of flamish girls, but she was pregnant and her mother locked her up in the castle La Mota.
After she had given birth to a son in March 1503, she still insisted to go after her husband. When her parents still didn't allow her to, she grew raging mad, fled from the castle, only half-dressed, and threw herself against the bars of the castle gate, screaming and cursing until she was exhausted. A year after her son's birth, she finally could travel to Flanders, only to find out that her husband had a mistress. Infuriated, she cut off the woman's hair and locked herself up in her room for days. She consulted Moorish sorcerers for love potions, in a desperate act of regaining her husband's attention, but without success. Following hunger strikes and outbreaks of anger would only push Philip farther away from her.
Upon Isabella's death in 1504, Joan was proclaimed Queen of Castile. But due to Joan's mental instability, both her father and Philip tried to convince her to hand over the government to them and eventually even cooperated in trying to declare her incompetent to rule without her knowing. The couple returned to Spain in January 1506, but hardly eight months later, Philip became seriously ill and died at the age of 28. Joan was inconsolable and her love for him grew even bigger. She would not leave his body and had to be dragged away from it eventually. Rumors go that she would have opened to coffin every night from then on and carressed Philip's remains. Worse rumors even tell she took the body from the coffin and kept it in her bed. Fact is that she would not allow the coffin to be moved away from her; it had to be kept in a nearby church so she could visit her husband every day, and when she travelled, she would take the coffin with her.
In 1509, Joan was taken to the convent in the castle of Tordesillas on her father's orders, where she would stay under close watch of the nuns. Her elder children were sent to the Low Countries and were put under the guard of Margaret of Austria, Philip's sister. Her youngest daughter Catalina however, stayed with Joan, since she would not let go of her. She already had denied any help at giving birth to the child, and now she didn't tolerate anyone near the girl. She seemed to consider her daughter as a last touchable relic of her lost husband.
She continued to live in seclusion, only appearing in public when it was absolutely necessary, and not anymore after 1520. Her mental state only got worse: she neglected her personal hygiene, lapsed into long periods of apathy and could get aggressive all of a sudden. She died in the convent at the age of 75 after having lived in captivity for 46 years.
But we have to question: was she really mad, or was her madness just a tool of the men in court to keep the power in male hands? We will never know.