His romantic involvement with British actress Vanessa Redgrave has continued for 40 years. In 1969, they had a son, Carlo Gabriel Sparanero (known professionally as Carlo Nero), a screenwriter and director. On December 31, 2006, they married.
In 1987, while filming in Cartagena, (Colombia) he was involved in an affair with Mauricia Mena and fathered a son named Franquito.
In 1967, he appeared in his first English language film, Camelot as Lancelot, where he met his future romantic partner, Vanessa Redgrave. Following this he appeared in the mafia film Il giorno della civetta opposite Claudia Cardinale released in 1968.
A lack of proficiency in English tended to limit these roles, although he also appeared in other English language films including The Virgin and the Gypsy (1970), Force 10 from Navarone (1978), Enter the Ninja (1981) and Die Hard 2 (1990).
Although often typecast in films like Los amigos (1972) or Keoma (1976) he has attempted an impressive range of characters, such as Abel in John Huston's epic The Bible: In The Beginning (1966), the humiliated engineer out for revenge in Street Law, and the gay lieutenant in Querelle (1982). He has appeared in almost 150 films, and has written, produced and starred in one: Jonathan degli orsi (1993).
More recently, he starred in Hungarian director Gábor Koltay's Honfoglalás (Conquest) in 1996, and subsequently in Koltay's Sacra Corona (Holy Crown) in 2001.