Pierre Rainier Stefano Casiraghi (born 5 September 1987, Centre Hospitalier Princesse Grace in Monte Carlo, Monaco) is the younger son of Caroline, Princess of Hanover, and her second husband, Stefano Casiraghi.
He is named after his maternal great-grandfather, Prince Pierre of Monaco, his maternal grandfather, Prince Rainier III of Monaco, and his father. His godparents are his uncle Prince Albert and the late Laura Sabatini Casiraghi, the wife of his uncle Daniele Casiraghi). Laura Sabatini Casiraghi died in October 2009 and her funeral in the locality of Fino Mornasco was attended by her godson, his mother, and his siblings.
Pierre was just over three years old at the time of his father's death in a boating accident. He spent his earliest years, after his father's death, living at his mother's farmhouse in the quaint town of Saint-Rémy-de-Provence.
He has two older siblings: Andrea Albert Pierre Casiraghi and Charlotte Marie Pomeline Casiraghi, and one younger half-sister, HRH Princess Alexandra of Hanover.
Besides French, it is known that he is fluent in Italian, English, and knows some German. He also plays the saxophone.
Pierre Casiraghi is third in line to the throne of Monaco, following his mother and brother. In February 2012 he made the news for allegedly being hospitalized after a brawl at a New York City bar.