Original: Until the birth of Prince Hisahito, son of Prince Akishino, on September 6, 2006, there was a potential succession problem, since Prince Akishino was the only male child to be born into the imperial family since 1965.
Simplified: Until the birth of a son to Prince Akishino on September 6, 2006, there was a potential succession problem. No male child had been born into the imperial family since Prince Akishino in 1965.