Japanese Emperor Naruhito and Empress Masako left for Britain on a government plane Saturday to attend Queen Elizabeth II's state funeral, marking the couple's first trip abroad since he ascended the Chrysanthemum Throne in 2019.

For the empress, who has long been battling a stress-induced illness, it is also her first overseas trip since she attended the coronation of Tonga's King Tupou VI in 2015.

Emperor Naruhito and Empress Masako are pictured with their daughter Princess Aiko at the Imperial Palace on Sept. 17, 2022, before the imperial couple's departure for Britain to attend Queen Elizabeth II's state funeral. (Pool photo)(Kyodo)

Japanese emperors do not traditionally attend funerals and the couple's attendance at the funeral of Britain's longest-reigning monarch on Monday will be only the second time, after then Emperor Akihito and his wife, Empress Michiko, traveled to Belgium for the funeral of King Baudouin in 1993.

The rare trip reflects the deep bond between the British royal family and the Japanese imperial family over the past decades. The attendance was decided after the Japanese government confirmed the emperor's intention following an invitation for two representatives extended by the British government, according to the Imperial Household Agency.

Japanese Prime Minister Fumio Kishida, who is set to attend the U.N. General Assembly next week, will not be present at the funeral.

The emperor and empress, wearing a dark suit and a gray dress, respectively, were seen exchanging words with their daughter Princess Aiko before they left the Imperial Palace in a vehicle in the morning for Tokyo's Haneda airport.

The couple bowed once before entering the plane to Crown Prince Fumihito, senior agency officials and others who were at the airport to send them off.

The two are scheduled to arrive at London Stansted Airport on Saturday afternoon and stay at Claridge's hotel during their visit. They are expected to return home on Tuesday.

During Queen Elizabeth's 70-year reign until her death at age 96 on Sept. 8, the British royal family and the Japanese imperial family maintained friendly relations for three generations, including the current emperor's grandfather and father.

As crown prince, former Emperor Akihito attended Queen Elizabeth II's 1953 coronation in London on behalf of Emperor Hirohito, posthumously known as Emperor Showa, who visited Britain in 1971.

The queen visited Japan in 1975. Emperor Akihito made his first visit as a monarch to Britain in 1998. He also attended the queen's Diamond Jubilee celebrations in 2012 to commemorate her 60th year on the throne.

The British royal family invited Emperor Naruhito and Empress Masako to visit Britain after he ascended the throne in May 2019 upon his father's abdication, but the plan was canceled due to the coronavirus pandemic.

A close aide to the emperor said he has been recalling his warm meetings with the queen while he was studying at Oxford.

His statement conveyed by the agency last week said, "I express my heartfelt sorrow and deep sadness."

"From my heart, I declare my gratitude and esteem for her many achievements and contributions," it said.