Englishman Alun Morgan bemused doctors after he woke up speaking fluent Welsh and no English following a severe stroke. He was soon diagnosed with aphasia.
Alun Morgan, 81, was evacuated to Wales during the Second World War but left 70 years ago.
During his time there he was surrounded by Welsh speakers but never learned the language himself.
Mr Morgan recently suffered a stroke, but when he regained consciousness three weeks later, doctors discovered he was speaking Welsh and could not remember any English.
Doctors diagnosed Mr Morgan with aphasia, a form of brain damage which causes a shift in the brain's language centre.
It is thought that the Welsh Mr Morgan heard as a boy had sunk in without him knowing and was unlocked after he suffered the stroke.