Her Serene Highness Princess Antoinette, Baroness of Massy (Antoinette Louise Alberte Suzanne Grimaldi) (b. 28 December 1920) is a member of the royal family of Monaco and the elder sister of the late Prince Rainier III. Her parents were Pierre de Polignac and Princess Charlotte, Duchess of Valentinois.

Three children were born to Princess Antoinette and her lover Alexandre Noghès, the Monegasque-born heir to a cigarette manufacturing fortune: Elisabeth-Anne (1947-), Christian Louis, (1949-), and Christine Alix (1951-). The parents subsequently married in Genoa on December 4, 1951 and divorced in 1954. Their children bear the title "Baron/Baroness de Massy".

Her second husband, Jean-Charles Rey , a writer, was married to her from 1961 to 1973.

Her third husband was John Gilpin, a renowned British ballet dancer, whom she married on July 28, 1983. He died the following September.