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The eldest grandchild of Rainier III, Prince of Monaco, and his wife, former American actress Grace Kelly, Casiraghi was named after his father's childhood friend, his maternal uncle Prince Albert and his maternal great-grandfather Prince Pierre, Duke of Valentinois. Casiraghi's godparents are his maternal aunt Princess Stéphanie and his paternal uncle, Marco Casiraghi. His sister Charlotte was born on 3 August 1986, and his brother Pierre on 5 September 1987.