Question: Andrea Albert Pierre Casiraghi, is the elder son of Caroline, Princess of Hanover, and her second husband Stefano Casiraghi, and is the eldest grandchild of Rainier III, Prince of Monaco, and which American actress, who became Princess of Monaco after marrying Prince Rainier III, in April 1956?
Context: Andrea Albert Pierre Casiraghi (born 8 June 1984) is the elder son of Caroline, Princess of Hanover, and her second husband Stefano Casiraghi.  He is the eldest grandchild of Rainier III, Prince of Monaco, and American actress Grace Kelly.  Casiraghi is currently fourth in the line of succession to the Monegasque throne, following his twin cousins and mother. Caroline, Princess of Hanover (Caroline Louise Marguerite Grimaldi; born 23 January 1957), is the eldest child of Rainier III, Prince of Monaco, and American actress Grace Kelly.  She is the elder sister of Prince Albert II and Princess Stéphanie.  Until the births of her niece and nephew Princess Gabriella and Prince Jacques of Monaco in December 2014 she had been heir presumptive to the throne of Monaco since 2005, a position which she previously held from 1957 to 1958. Princess Antoinette of Monaco, Baroness of Massy (Antoinette Louise Alberte Suzanne Grimaldi; 28 December 1920 – 18 March 2011) was a member of the princely family of Monaco and the elder sister of Prince Rainier III and aunt of Albert II, Prince of Monaco.  Her parents were Count Pierre de Polignac and Princess Charlotte, Duchess of Valentinois. Monaco is a city and independent state located in the south of France, along the Mediterranean coast.  The country has long been under the control of the Grimaldi family, who have encouraged musical development.  Prince Rainier III introduced the Prince Rainier III Prize for Musical Composition to reward Monegasque musicians. The Fondation Prince Pierre was established by Prince Rainier III of Monaco in February 1966 to promote culture and the arts through the creation and the awarding of prizes.  Prince Rainier III created the foundation in tribute to his father, Pierre de Polignac a great patron of the arts. Grace Patricia Kelly (November 12, 1929September 14, 1982) was an American actress who became Princess of Monaco after marrying Prince Rainier III, in April 1956. Alice Heine (February 10, 1858 – December 22, 1925), styled HSH The Princess of Monaco, previously The Duchess of Richelieu, was the American-born second wife of Prince Albert I of Monaco, a great-grandfather of Prince Rainier III of Monaco and great-great grandfather of reigning prince Albert II of Monaco.  Marcel Proust used her as a model for the "Princesse de Luxembourg" in his novel, "In Search of Lost Time".  Her first husband was the Duke of Richelieu, and one of the titles of her second husband was the Duke of Mazarin; she was thus unique in bearing the titles of both Cardinal Richelieu and Cardinal Mazarin. Albert II (Albert Alexandre Louis Pierre Grimaldi; born 14 March 1958) is the reigning monarch of the Principality of Monaco and head of the princely house of Grimaldi.  He is the son of Prince Rainier III and the American actress Grace Kelly.  Prince Albert's sisters are Caroline, Princess of Hanover, and Princess Stéphanie.  In July 2011, Prince Albert married Charlene Wittstock. Pierre Rainier Stefano Casiraghi (born 5 September 1987) is the younger son of Caroline, Princess of Hanover, and her second husband, Stefano Casiraghi.  His maternal grandparents were Rainier III, Prince of Monaco, and American actress Grace Kelly.  Casiraghi is seventh in the line of succession to the Monegasque throne, following his twin cousins, his mother, brother Andrea, nephew Alexandre, and his niece India Casiraghi. Charlotte Marie Pomeline Casiraghi (born 3 August 1986) is the second child of Caroline, Princess of Hanover, and Stefano Casiraghi, an Italian industrialist.  She is ninth in line to the throne of Monaco.  Her maternal grandparents were Rainier III, Prince of Monaco, and American actress Grace Kelly.  She is named after her maternal great-grandmother, Princess Charlotte, Duchess of Valentinois.
Answer: Grace Kelly