Princess Caroline’s Husband Killed as Boat Flips Over : Monaco: Tragedy revisits the royal family: Princess Grace died in car accident eight years ago.

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 that Casiraghi and his co-pilot, Patrice Innocenti, drove their 42-foot catamaran, the Pinot di Pinot, straight into a wave at 93 m.p.h. during a morning run for the World Offshore Championships.

The boat flipped over, ejecting Innocenti. 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.

“He surely didn’t have time to look out and, at that speed, stuck under the boat, must have been killed by the blow,” said another competitor, Michel Karsten.

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

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

Weather conditions off Saint-Jean-Cap-Ferrat, between Monaco and Nice, France, were described as normal. The accident occurred as the second stage of the race opened Wednesday. Organizers canceled the day’s events but did not say when or if they would be rescheduled.

The accident was the worst blow to Monaco’s ruling family since Princess Grace, the American actress who gave up Hollywood to marry Prince Rainier III, died in 1982. Caroline’s younger sister, Princess Stephanie, also was injured in that car crash.

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.

She said she married again because she was in love and knew an annulment--first sought in 1981--would take a long time.

“I wanted a real home and children,” she was quoted as saying. “It was difficult for my conscience, but I was overwhelmed by the desire to have children. Surely that can be understood from a Christian point of view.”

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 couple were reported to have a close relationship and divided their time between Monaco and Casiraghi’s home outside Milan, Italy.

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.

Casiraghi studied economics at the University of Bocconi in Milan but dropped out before getting his degree. He had a passion for offshore racing. Since 1984, he had won 12 races, including last year’s world championships off Atlantic City, N.J.