This is the third marriage for the eldest daughter of the late Princess Grace, the former Hollywood actress Grace Kelly, who was killed in a 1982 car accident.
Caroline was first married in 1978 to French playboy Philippe Junot, a union which drew the disapproval of her parents and the constant attention of the international press. The couple divorced after two years of marriage.
Caroline's second marriage, to Italian Stefano Casiraghi, was a happier union. Married in 1983, the couple had three children before he was killed in a boating accident in 1990.
The princess' father, Prince Rainier, 75; her brother, Prince Albert, 40, and her children, Andrea, 14, Charlotte, 12, and Pierre, 11, were on hand at Saturday's wedding. The bride's sister, Princess Stephanie, 33, was not. No explanation was given.
Stephanie, who had a baby girl born out of wedlock in July and has two children from her first marriage, divorced her second husband, former bodyguard Daniel Ducruet, in 1996 after he was photographed cavorting poolside at a Riviera villa with a former Miss Topless Belgium.
There had been no advance public announcement of Caroline's marriage plans Saturday, though French newspapers had reported a wedding might be imminent as Caroline was said to be three months pregnant. In accordance with a historical agreement between the British and German royal families, the bridegroom was required to ask Queen Elizabeth II for permission to marry Caroline. It was the second marriage for the German prince.
Prince Ernst, 44, and his Swiss wife of 16 years, Princess Chantal, were divorced in London in September 1997. The couple had two sons, Ernst, 15, and Christian, 13.
The great-grandson of German Kaiser Wilhelm II, Ernst left school at 15 to work on a farm after disputes over smoking and the length of his hair.