With a grand traditional betrothal ceremony on Saturday, Japanese Princess Sayako was formally engaged to a common civil servant.

The 35-year-old princess is the only daughter of Japan's emperor, and will lose his royal identity after her marriage according Japan's law.

Her 35-year-old fiance, Yoshiki Kuroda, is an employee with the Tokyo metropolitan government.

They are expected to marry sometime after the summer, the Imperial Household Agency said earlier.

In the privately held ceremony that lasted about 15 minutes at the Imperial Residence, a messenger from Kuroda formally conveyed Kuroda's proposal to marry Princess Sayako to Grand Steward Toshio Yuasa of the Imperial Household, Kyodo News reported.

The messenger also offered traditional engagement gifts of two fresh sea breams, three bottles of sake and two sets of silk, the agency said. Sea breams are given as gifts in Japan to mark auspicious events.

The grand steward then reported to the emperor and empress in a different room, also attended by the princess, about the proposal and the imperial couple granted approval.

The couple became formally engaged when the grand steward returned to the messenger and said that the princess and her parents accepted the offer of marriage.

Wearing a white long dress, Princess Sayako bowed to a flock of reporters and photographers, and responded to their congratulations earlier in the morning before entering the Imperial Residence.

The couple reportedly has known each other since their childhood, as Kurado is a close friend of the princess' elder brother Prince Akishino, and decided to marry last summer.

They are looking for an apartment in Tokyo for their new residence while considering security and other points, Kyodo said.