Princess Antoinette, Baroness of Massy

On 18 March 2011 Princess Antoinette died at The Princess Grace Hospital Centre, aged 90. Her funeral took place on 24 March 2011. She is buried in the Chapel of Peace in Monaco beside her parents, her daughters Elizabeth-Ann and Christine-Alix, her last husband John Brian Gilpin and her nephew by marriage, Stefano Casiraghi.

Upon the accession of Albert II in 2005, Antoinette and her descendants lost their place in the line of succession to the Monegasque throne, which is limited to the current sovereign's descendants, siblings, and siblings' descendants.

Rainier's marriage to Grace Kelly in 1956 and the arrival of his heirs, Princess Caroline in 1957 and Prince Albert in 1958, effectively scuttled Antoinette's plans. She was removed from the Palace by her sister-in-law, Princess Grace, and thereafter was estranged from the princely family for many years.

She was known to be somewhat eccentric and was described as "completely mad" by her servants. Having been banished from Monaco in the late 1950s, she lived down the coast from Monaco at Èze, with a large collection of dogs and cats. She was the president of Monaco's Society for the Protection of Animals and Refuge and a patron of the UK-based Battersea Dogs and Cats Home.

Princess Antoinette had a long-term liaison with Alexandre-Athenase Noghès, a Monegasque-born attorney and international tennis champion, in the mid-1940s. The couple had three children born out-of-wedlock who were legitimated by their parents' eventual marriage and, henceforth, included in the line of succession to the Monegasque Throne until the death of Antoinette's brother, Prince Rainier III, in 2005; Elizabeth Ann de Massy (1947–2020), Christian Louis de Massy (born 1949), and Christine Alix de Massy (1951–1989).

Princess Antoinette, Baroness of Massy (Antoinette Louise Alberte Suzanne Grimaldi; 28 December 1920 – 18 March 2011) was a member of the princely family of Monaco. She was the elder sister of Prince Rainier III. Her parents were Count Pierre de Polignac and Charlotte, Hereditary Princess of Monaco and Duchess of Valentinois.