On 6 September 2006, the Emperor celebrated the birth of his first grandson, Prince Hisahito, the third child of the Emperor's younger son. Prince Hisahito is the first male heir born to the Japanese imperial family in 41 years (since his father Prince Akishino) and could avert a possible succession crisis as the Emperor's elder son, the Crown Prince Naruhito, has only one daughter, Princess Aiko. Under Japan's male-only succession law, Princess Aiko is not eligible for the throne.