Crown Prince Akishino and Crown Princess Kiko left Tokyo on Thursday for Britain to attend the coronation of the country's King Charles III on Saturday.
It is the couple's first official visit to Britain and their first time to attend a foreign royal coronation. Emperor Naruhito does not attend foreign royal coronations in line with custom, leaving his younger brother to attend in his stead, according to the Imperial Household Agency.
The couple departed from Tokyo's Haneda airport on a government-chartered plane and will arrive at London Stansted Airport later in the day and stay at a hotel in the city.
The crown prince and the crown princess left their residence by car as the couple's second daughter, Princess Kako, and son, Prince Hisahito, saw them off.
The couple greeted the British ambassador to Japan and Imperial Household Agency officials before boarding their airport.
On Friday, the couple will meet with Japanese expatriates at the official residence of the Japanese ambassador to Britain in the morning and attend a reception hosted by King Charles III at Buckingham Palace in the afternoon.
After attending the coronation at Westminster Abbey on Saturday, the couple will leave Britain later the same day. They are set to return home Sunday afternoon.
In 1953, then-Crown Prince Akihito, now the emperor emeritus, attended the coronation of Britain's Queen Elizabeth II on behalf of then Emperor Hirohito, posthumously known as Emperor Showa.
Current Emperor Naruhito and Empress Masako attended the funeral of Queen Elizabeth II in September last year.