In 1502, Philip, Joanna and a large part of the Burgundian court travelled to Spain to receive fealty from the Cortes of Castile as heirs, a journey chronicled in intense detail by Antoon I van Lalaing (French: Antoine de Lalaing), the Future Stadtholder of Holland and Zeeland. Philip and the majority of the court returned to the Low Countries in the following year, leaving a pregnant Joanna behind in Madrid, where she gave birth to Ferdinand, later Holy Roman Emperor. Although Joanna was deeply in love with Philip, their married life was rendered extremely unhappy by his infidelity and political insecurity, during which time he constantly attempted to usurp her legal birthrights of power. This led in great part to the rumors of her insanity due to reports of depressive or neurotic acts committed while she was being imprisoned or coerced by her husband, rumors that benefited Philip politically. Most historians now agree she was merely clinically depressed at the time, not insane as commonly believed. Before her mother's death, in 1504, husband and wife were already living apart.
In 1504, Philip's mother-in-law, Queen Isabella of Castile, died, leaving the Crown of Castile to Joanna. Isabella I's widower and former co-monarch, King Ferdinand II, endeavored to lay hands on the regency of Castile, but the nobles, who disliked and feared him, forced him to withdraw. Philip was summoned to Spain, where he was recognized as king.
However, Philip died suddenly at Burgos, apparently of typhoid fever, on 25 September 1506, although a poisoning (assassination) was widely spoken of at the time, and is what his wife believed to be the cause of Philip's death. His wife supposedly refused to allow his body to be buried or part from it for a while. Philip I is entombed at the Royal Chapel of Granada (Capilla Real de Granada), alongside his wife, and her parents Isabella I and Ferdinand II.
