Roussos, the Egyptian-born singer, became popular in the 1960s and 1970s and sold about 60 million records globally.
He was best known for his solo hits, including Forever and Ever, Goodbye and Quand je t'aime.
He was also a member of progressive rock group Aphrodite's Child. It is worth noting that the late singer had been in the private hospital with an undisclosed illness for some time.