Roussos, who died on Sunday (local time), was part of the progressive rock group Aphrodite's Child but was best known for his solo hits, among them "Forever and Ever", "Goodbye", "Quand je t'aime" and "Happy to Be on an Island in the Sun".
"Forever and Ever" was used in British director Mike Leigh's 1977 television play "Abigail's Party" and Roussos was also the subject of a British documentary "The Roussos Phenomenon" in the mid-1970s.
Aphrodite's Child bandmate Vangelis, in a statement quoted by the BBC, said: "Demis my friend. I have just arrived in London and I've been told that you decide to take the long voyage, I'm shocked because I can't believe that this happened so soon.
"Nature gave you this magic voice of yours which made millions of people around the world very happy."
Roussos was born on June 15, 1946, and was raised in Alexandria, Egypt, by his Greek engineer father and his Egyptian mother of Italian heritage. The family moved to Greece during the Suez Crisis and Roussos started his singing career at the age of 17 with a band called The Idols, where he first met Vangelis.
