Upon the death of her mother in November 1504, Joanna became Queen regnant of Castile and her husband jure uxoris its king.
Joanna's father, Ferdinand II, lost his monarchical status in Castile although his wife's will permitted him to govern in Joanna's absence or, if Joanna was unwilling to rule herself, until Joanna's heir reached the age of 20.

Ferdinand refused to accept this; he minted Castilian coins in the name of "Ferdinand and Joanna, King and Queen of Castile, León and Aragon," and, in early 1505, persuaded the Cortes that Joanna's "illness is such that the said Queen Doña Joanna our Lady cannot govern".
The Cortes then appointed Ferdinand as Joanna's guardian and the kingdom's administrator and governor.

Joanna's husband, Philip the Handsome, was unwilling to accept any threat to his chances of ruling Castile and also minted coins in the name of "Philip and Joanna, King and Queen of Castile, Léon and Archdukes of Austria, etc."
In response, Ferdinand embarked upon a pro-French policy, marrying Germaine de Foix, niece of Louis XII of France (and his own great-niece), in the hope that she would produce a son to inherit Aragon and perhaps Castile.

Ferdinand's remarriage merely strengthened support for Philip and Joanna in Castile, and in late 1505, the pair decided to travel to Castile.
Leaving Flanders on 10 January 1506, their ships were wrecked on the English coast and the couple were guests of Henry, Prince of Wales, later Henry VIII and Joanna's sister Catherine of Aragon at Windsor Castle.
They weren't able to leave until 21 April, by which time civil war was looming in Castile.

Philip apparently considered landing in Andalusia and summoning the nobles to take up arms against Ferdinand in Aragon.
Instead, he and Joanna landed at A Coruña on 26 April, whereupon the Castilian nobility abandoned Ferdinand en masse.
Ferdinand met Philip at Villafáfila on 27 of June 1506 for a private interview in the village church.
To the general surprise Ferdinand had unexpectedly handed over the government of Castile to his "most beloved children", promising to retire to Aragon.
Philip and Ferdinand then signed a second treaty secretly, agreeing that Joanna's "infirmities and sufferings" made her incapable of ruling and promising to exclude her from government and deprive the Queen of crown and freedom.

Ferdinand promptly repudiated the second agreement the same afternoon, declaring that Joanna should never be deprived of her rights as Queen Proprietress of Castile.
A fortnight later, having come to no fresh agreement with Philip, and thus effectively retaining his right to interfere if he considered his daughter's rights to have been infringed upon, he abandoned Castile for Aragon, leaving Philip to govern in Joanna's stead.
Upon the death of her mother in November 1504, Joanna became Queen regnant of Castile and her husband jure uxoris its king. Joanna's father, Ferdinand II, lost his monarchical status in Castile although his wife's will permitted him to govern in Joanna's absence or, if Joanna was unwilling to rule herself, until Joanna's heir reached the age of 20.
Ferdinand refused to accept this; he minted Castilian coins in the name of "Ferdinand and Joanna, King and Queen of Castile, León and Aragon," and, in early 1505, persuaded the Cortes that Joanna's "illness is such that the said Queen Doña Joanna our Lady cannot govern". The Cortes then appointed Ferdinand as Joanna's guardian and the kingdom's administrator and governor.
Joanna's husband, Philip the Handsome, was unwilling to accept any threat to his chances of ruling Castile and also minted coins in the name of "Philip and Joanna, King and Queen of Castile, Léon and Archdukes of Austria, etc." In response, Ferdinand embarked upon a pro-French policy, marrying Germaine de Foix, niece of Louis XII of France (and his own great-niece), in the hope that she would produce a son to inherit Aragon and perhaps Castile.
Ferdinand's remarriage merely strengthened support for Philip and Joanna in Castile, and in late 1505, the pair decided to travel to Castile. Leaving Flanders on 10 January 1506, their ships were wrecked on the English coast and the couple were guests of Henry, Prince of Wales, later Henry VIII and Joanna's sister Catherine of Aragon at Windsor Castle. They weren't able to leave until 21 April, by which time civil war was looming in Castile.
Philip apparently considered landing in Andalusia and summoning the nobles to take up arms against Ferdinand in Aragon. Instead, he and Joanna landed at A Coruña on 26 April, whereupon the Castilian nobility abandoned Ferdinand en masse. Ferdinand met Philip at Villafáfila on 27 of June 1506 for a private interview in the village church. To the general surprise Ferdinand had unexpectedly handed over the government of Castile to his "most beloved children", promising to retire to Aragon. Philip and Ferdinand then signed a second treaty secretly, agreeing that Joanna's "infirmities and sufferings" made her incapable of ruling and promising to exclude her from government and deprive the Queen of crown and freedom.
Ferdinand promptly repudiated the second agreement the same afternoon, declaring that Joanna should never be deprived of her rights as Queen Proprietress of Castile. A fortnight later, having come to no fresh agreement with Philip, and thus effectively retaining his right to interfere if he considered his daughter's rights to have been infringed upon, he abandoned Castile for Aragon, leaving Philip to govern in Joanna's stead.
Joanna of Castile