The Duchess of Alba, whose full name is Maria del Rosario Cayetana Alfonsa Victoria Eugenia Francisca Fitz-James Stuart y de Silva, married a 61-year-old commoner in a low-key affair.
Only about 30 people were invited to the ceremony at Palacio de las Duenas, her 15th-century residence in the cobblestoned old quarter of Seville.
The duchess and her groom came out afterwards to greet well-wishers and treated them to a flamenco dance.
Estimates of her wealth range from $800 million to $4.7 billion, and the family treasure boasts paintings by Goya and Velasquez, a first edition copy of Cervantes "El Quixote," and letter written by Christopher Columbus.
Her six children, all from her first marriage, reportedly balked when the idea of marriage emerged. In July of this year the duchess assigned them and her grandchildren juicy chunks of her vast estate, like mansions and palaces, in an effort to appease them and clear her way to the altar.
The New York Times called her first wedding in 1947 "the most expensive wedding in the world" at the time.
The Associated Press contributed to this report.