Boris Johnson will be the fifth prime minister since the Second World War to have been educated at Eton College.
The other four to attend the independent, fee-paying boarding school were David Cameron (prime minister from 2010-16), Alec Douglas-Home (1963-64), Harold Macmillan (1957-63) and Anthony Eden (1955-57).
Like Boris Johnson, all of them were Conservative prime ministers.
It means one third of the UK’s 15 prime ministers since 1945 are Old Etonians – the name given to former pupils of the college.
Three other post-war PMs attended independent schools: Clement Attlee (Haileybury), Winston Churchill (Harrow) and Tony Blair (Fettes).
The rest, including outgoing Prime Minister Theresa May, all attended grammar schools.
Eton College, near Windsor in Berkshire, has a history of producing prime ministers that stretches back to Robert Walpole in the early 18th century.
Walpole is widely regarded by historians as the first prime minister of Great Britain and the person who did most to shape the role into what we still recognise it to be today: the most important individual in the government.
Other Eton-educated PMs include William Pitt the Elder (prime minister from 1766-68); Arthur Wellesley, 1st Duke of Wellington (twice prime minister in the early 19th century); William Gladstone (four-time prime minister in the late 19th century); and Arthur Balfour (1902-05).