As reported by Agence France-Presse (AFP), Japan’s former Prime Minister made the announcement after a recent JRFU Board meeting.

He put it partly down to health concerns having undergone surgery several times due to cancer.

"Mr Mori expressed his intention to resign because of his age and condition as well as his job at the Olympics and Paralympics," a JRFU spokesman told AFP.

"But his resignation won't affect our hosting of the World Cup.

"Mr Mori has said he will continue supporting the World Cup but expressed hope that young people should take the initiative in pushing for the sport."

The spokesman added that a replacement for Mori has not been decided.

But Kyodo News reports that by making the announcement well in advance of June’s elections for JRFU offices, Mori is opening the door for chairman Masaru Okamura to depart by moving up to the position as the next honorary chairman.

Mori has reportedly said that with Japan losing its franchise in the Southern Hemisphere’s Super Rugby competition, the Tokyo-based Sunwolves, after 2020, and the future of the Japan Top League in doubt, the country critically needs a vision for the sport post-World Cup.

The Sunwolves were introduced in 2016 in an attempt to bring rugby to new markets but Super Rugby organisers chose last month to boot them out after next year.

Mori served as JRFU chairman for 10 years until April 2015, when he announced his intention to stand down from his role to concentrate on organising the Tokyo 2020 Olympic and Paralympic Games and was replaced by Okamura. 

A month earlier, he revealed that he had been successfully treated for cancer and with Japan set to host the Rugby World Cup for the first time in 2019, he told Kyodo News "it isn't good" that he continues to take responsibility for two major sporting events.

Mori, one of Japan's most unpopular Prime Ministers, had been a controversial appointment in January 2013 to head Tokyo 2020.

At the time he joked: "I am destined to live five or six more years if I am lucky."