Diamond was born in London but his parents died during World War II, and he was adopted aged five by a white Welsh family - the first Black person ever seen by many people in his new village of Llansaint.
He trained as a nurse and physiotherapist, played rugby for Llanelli, and is now an actor, most notably in Galw Gari Tryfan, Pobl y Cwm and Dinas on the Welsh television channel S4C, and on the stage.