Emperor Naruhito, who is on an official visit to Britain, on Monday attended a reception in London hosted by five Japanese-British friendship organizations including the Japan Society.
At the reception, the emperor was welcomed by the Duke of Gloucester, cousin of the late Queen Elizabeth II and patron of the Japan Society.
"It is my wish that our bilateral ties will grow even stronger in the years to come, building on such firm foundations as people-to-people connections," the emperor said in English following a speech by Bill Emmott, the society's chairman.
About 400 people attended the event, and the emperor engaged with them warmly.
According to the Imperial Household Agency, on Monday evening the emperor met privately with the wife of a now-deceased security guard for the emperor during his studies in Britain.
Earlier on Monday, the emperor visited a flood prevention facility on the River Thames in the suburbs of London.
The emperor, who studies water issues as his lifework, entered the control room of the Thames Barrier wearing a helmet, asked questions and checked how it works.
The Thames Barrier consists of 10 moveable sluice gates to protect the British capital from storm surges from the North Sea.
The emperor did research on the history of transportation on the River Thames when he was studying at the University of Oxford. Since then, he has repeatedly visited water-related facilities.
Empress Masako rested at a hotel ahead of welcome events as a state guest starting Tuesday.
With your current subscription plan you can comment on stories. However, before writing your first comment, please create a display name in the Profile section of your subscriber account page.