However, Joseph Ferdinand died on February 3, 1699, at the age of six, leaving the Spanish Succession uncertain again. His death was quite sudden, Joseph Ferdinand being gripped with seizures, vomiting and prolonged loss of consciousness. He was rumoured to have been poisoned, but nothing has been proven. He is buried in Brussels. With him the furthest line of descent possible from the marriage of Philip IV of Spain and his second wife and niece Mariana of Austria ended.