He was the eldest son of Francis Xavier Shields, a professional American tennis player and of the Italian Princess Donna Marina Torlonia di Civitella-Cessi, and through his mother he is a relative of such important and aristocratic Italian families like the Borgias, Medici, d'Este, di Savoia among others. He married firstly in 1964 (now divorced) the californian Maria Theresia Schmonn (more known as as Brooke Shields manager like Terri Shields), and then he married again in 1970 to Diana Lippert. He had four daugthers: Brooke Shields, Marina Shields, Olimpia Shields and Christina Shields.