Stefano Casiraghi, the 30-year-old husband of Princess Caroline, was killed Wednesday when he flipped his speedboat while defending his title in a world championship race, the Royal Palace said.

Caroline, 33, was in Paris when she learned of the death of her Italian financier husband. She quickly left for Monaco, wearing black mourning clothes. It was the second tragedy to strike the Grimaldi family in eight years - Caroline's mother, Princess Grace, died after a car crash in 1982.Witnesses said Casiraghi and co-pilot Patrice Innocenti drove their catamaran, the Pinot di Pinot, straight into a wave at 93 mph during a morning run for the World Offshore Championships.

The 42-foot boat flipped over, ejecting Innocenti. But witnesses said Casiraghi remained strapped to his seat and bore the full impact of the vessel slamming into the water.

The two-engine, five-ton boat sank with Casiraghi aboard, witnesses said.

Emergency crews pulled both men from the water and rushed them to Princess Grace Hospital.

The hospital said Innocenti, the boat's driver, was being treated for his injuries.

Caroline married Casiraghi in a civil ceremony Dec. 29, 1983, under a portrait of her mother. The marriage followed an unhappy two-year union with French playboy Philippe Junot.

Caroline and Casiraghi had three children: a son Andrea, 6; Charlotte, 4; and Pierre, 3.

Caroline married the tall, blond Casiraghi after divorcing Junot but without obtaining a Roman Catholic Church annulment of the marriage.

The relatively low-profile lifestyle Caroline had enjoyed since marrying Casiraghi contrasted sharply with the weekly splash she made in celebrity magazines during the 1970s.

The fun-loving but steady Casiraghi ran a successful real estate firm in Milan as well as a retail export business. His father made his fortune in heating and air conditioning equipment.