Japan's Emperor Naruhito and Empress Masako will visit Britain as state guests in late June. They were formally invited by King Charles.
Sources say the Imperial couple is expected to stay for a week or so.
The Emperor and Empress will likely attend a welcome ceremony in London. Arrangements are also being made for a visit to their alma mater, Oxford University.
The visit to Britain will be the Imperial couple's third overseas trip since the Emperor was enthroned in 2019.
It will also be the third state visit to Britain by a Japanese Emperor and Empress. The first was in 1971, and the second in 1998.
Late British Queen Elizabeth II invited the Imperial couple to a state visit in 2020, but the plan was put on hold due to the coronavirus pandemic.
King Charles was diagnosed with cancer earlier this year. But in a statement on Friday, Buckingham Palace said he is now able to resume some public-facing duties.
Emperor Naruhito and Empress Masako will be King Charles' first state guests since he announced the start of his cancer treatment in February.