The Japanese emperor and empress are not the only royals flying into the UK to mark the passing of the late Queen, who made more overseas trips than any past British monarch.
The Telegraph has seen a list of more than 20 high-profile overseas royal family members expected to attend the funeral.
From Europe, attendance is expected from the King of the Belgians, the Queen of Denmark, the Hereditary Prince Alois of Liechtenstein, the Grand Duke of Luxembourg, and the Prince of Monaco, as well as the kings of the Netherlands, Norway, Spain and Sweden.
Others present will include the King of Bhutan, the Sultan of Brunei, the Crown Prince of Kuwait, the Malaysian Sultan, the Sultan of Oman, the Amir of the State of Qatar, the King of Tonga and the president of the UAE.
For Saudi Arabia, an acceptance has been received from King Salman bin Abdulaziz a-Saud. Invitations were sent to heads of states.
Crown Prince Mohammed bin Salman, widely seen by political commentators as the real power behind the throne, is also expected to be in the UK in the coming days.
He will deliver his country’s condolences to the Royal family after the death of the Queen, according to The Guardian, who referenced a source with knowledge. However, it is unclear if he will attend the funeral.
The Crown Prince, known as MBS, has not visited the UK since the murder of the Jamal Khashoggi, the Washington Post columnist, in October 2018, which triggered UK sanctions.