Because a female Grimaldi could inherit only if her husband was also a Grimaldi, Pierre de Polignac became Prince Pierre Grimaldi, Comte de Polignac on 18 March, 1920, the day before his religious marriage.
He married civilly 18 March 1920 in Monaco Princess Charlotte of Monaco, née Charlotte Louise Juilette Louvet, daughter of Louis II of Monaco and Marie Juliett Louvet. They were judicially separated 20 Mar 1930 at Paris, and divorced by ordinance of Prince Louis II 18 Feb 1933. Following the divorce, Charlotte took up residence at the Château de Marchais with René Gigier, one of France’s most infamous jewel thieves.
The Count and his wife had two children, Princess Antoinette of Monaco (b. 1920) and Rainier III of Monaco.