After receiving approval from the emperor, the princess has formally announced her engagement to a commoner, and, in doing so, has signaled the forfeiture of her royal status. Based on existing laws, female members of the imperial family must give up their status should they marry a commoner. The same law does not apply to male members of the family and has long been a source of controversy for the Japanese imperial family.

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The royal family is comprised of only 19 people, 14 of whom are women. In June, Japan’s parliament passed a historic bill that enabled the sitting monarch, Emperor Akihito, to abdicate, passing the throne to his eldest son, Crown Prince Naruhito. Yet Crown Prince Naruhito has no sons, meaning that the succession would pass on to his younger brother Akishino, Princess Mako’s father. He, in turn ,has only one son, Hisahito, who would then follow next in line. Unless Hisahito (who is currently 10 years old), has a son with his future wife, there will be no more eligible males to the throne, triggering a succession crisis and threatening the lineage of the imperial family.

With so few male members, the Japanese imperial family has heard calls for women to be allowed to inherit the throne or maintain their royal status in marriages to commoners. To traditionalists, female succession is unthinkable. Prime Minister Shinzo Abe initially placated such conservative members of his party earlier this year when he resisted a push to debate the idea. However, the formal announcement of Princess Mako’s engagement is expected to reignite discussion of the matter—if only to prevent the end of the imperial line.