He told Het Laatste Nieuws newspaper: "While my brothers were celebrated, I got a storage room above the garage as a bedroom. 'If only you had been a boy', my mother complained. I was tolerated, nothing more."

Mr Verhelst had hormone therapy in 2009, followed by a mastectomy and surgery to construct a penis last year. However, "none of these operations worked as desired", he said. "I was ready to celebrate my new birth, but when I looked in the mirror, I was disgusted with myself. My new breasts did not match my expectations and my new penis had symptoms of rejection. I do not want to be a monster."

He informed his family of his death by letter. "I had happy times, but the balance is on the wrong side," he said.

Prof Distelmans said: "He was in a situation with incurable, unbearable suffering. Unbearable suffering for euthanasia can be both physical and psychological."

Mr Verhelst's death will revive Belgium's debate over medical euthanasia as statistics show a 25 per cent increase this year, to 1432, in the number of cases. The country is one of only three in Europe, along with Holland and Luxembourg, that allows the practice.