The Athens Medical Association has launched an investigation into a private doctor’s office in central Athens where Greek singer Giorgos Mazonakis, 54, suffered cardiac arrest during a scheduled treatment before his death on Wednesday.

Greek musician Giorgos Mazonakis, 54, died in Athens after a reported cardiac arrest. His official cause of death has not yet been announced.

Greek pop star Giorgos Mazonakis, who also enjoyed a strong following among the Greek diaspora, has died of a heart attack after being rushed to a hospital in Athens. He was 54.