After wedding a playboy and a businessman, Princess Caroline of Monaco married a prince, exchanging vows Saturday with Ernst August of Hanover. The princess, a Roman Catholic, chose her 42nd birthday as the day for the civil ceremony with her longtime boyfriend, who is Protestant. Caroline’s father, Prince Rainier, announced the marriage. The bride wore an elegant light gray suit with gold buttons and a gold pin on her lapel, while her husband was dressed in a dark suit. In accordance with an historical agreement between the British and German royal families, the prince was required to ask Queen Elizabeth II for permission to marry Caroline. It was the second marriage for the German prince.