It is not clear whether any senior royals will attend the ceremony.
Mountbatten is the queen’s third cousin once removed, and the great-great-great grandson of Queen Victoria. However, his family name gives him a higher profile in British aristocratic circles; he is the great-nephew of Earl Mountbatten of Burma, the World War II naval commander who led Allied military forces in southeast Asia.
In a reflection of social change, royal attitudes to homosexuality have progressed since 1960 when Jeremy Fry, Lord Snowdon’s choice of best man for his wedding to Princess Margaret, was vetoed after it was discovered he had a conviction for a “minor homosexual offense.”
"In recent years I've been compassionate about what we can do to protect people from bullying, particularly online," he said. "Through this work, I've encountered a number of tragic stories about LGBT young people who have, sadly, felt unable to cope with the abuse and discrimination they face in their lives."
William also made history in May 2016 as the first British royal to be featured on the cover a gay magazine.