Princess Mako, the 25-year-old eldest daughter of Prince Akishino and his wife, Kiko, will become engaged to a man she met while attending the International Christian University in Tokyo.
The Imperial Household Agency will make an announcement on the planned engagement soon, according to sources.
The prospective fiance is Kei Komuro.
Princess Mako has already introduced him to her parents, and they have approved of the relationship, the sources said.
After graduating from university, Princess Mako has been engaged in official duties as an adult member of the Imperial family, including as honorary patron of the Japan Tennis Association.
She currently is an affiliate researcher at the University Museum of the University of Tokyo.
Once she gets married, she will leave the Imperial family.
