But in Carlos [the Second, of Spain] the tactic [incestuous marriage from within the Hapsburg family] had produced a near monstrosity. It wasn’t enough that seven of his eight great-grandparents descended from a single female ancestor; she had, in addition, to be mad.
Her name was Juana, a plump-faced, intelligent, unusually well read daughter of Ferdinand and Isabella of Spain who had married Philip I [of Spain] and bit by bit grew obsessed with him. In his absence she’d fall into a kind of trance, staring dully into space and breaking out into fits of hysterical screaming. Soon the windows of her room were barred, and even her parents locked her away in a strong castle when she came to visit. When Philip died, she succumbed to her other world completely; she began a funeral march unlike any other before or after in the annals of royal madness. Philip’s heart was removed and sent home to Flanders, and his body was packed into a coffin. But Juana refused to relinquish him; instead processions of men with torches, armed guards, and chanting monks preceded the coffin as the queen journeyed from castle to castle through her realm.
Juana never let the coffin out of her sight, and every day she’d open it and inspect the body for any signs of renewed life; disappointed, she’d kiss Philip and close the lid once again. Women along the roads were kept out of view; Juana believed they could still tempt Philip away from her. The macabre procession went on for weeks.
Source:
Carlos II (Charles II of Spain)
Joanna of Castile / Juana la Loca (Joanna the Mad)
There are not many lovefilled, passionate marriages in European history, but I guess nobody can accuse Joanna of not loving her husband.