Maria del Rosario Cayetana Fritz-James Stuart passed away at her Duenas Palace in the southern city of Seville on Thursday morning, a family spokesman told AFP.
She had been moved to her home on Tuesday night after being hospitalised with pneumonia. The socialite is survived by her husband, who is 24 years her junior.
Known for her frizzy hair and colourful dress sense, Maria del Rosario Cayetana Fitz-James Stuart owned swathes of real estate, palaces, great houses and treasures including paintings by Great Masters from Goya to Velazquez.