She passes Queen Victoria, her great-great-grandmother, who was on the throne for 63 years and 7 months.

Prime Minister David Cameron said on Wednesday that millions on Britons would celebrate the Queen’s “historic moment.”

“Over the last 63 years, Her Majesty has been a rock of stability in a world of constant change and her selfless sense of service and duty has earned admiration not only in Britain, but right across the globe,” Mr. Cameron said.

“It is only right that today we should celebrate her extraordinary record, as well as the grace and dignity with which she serves our country.”

Buckingham Palace marked the event by releasing an official photograph of the Queen taken by Mary McCartney, a photographer who is the daughter of former Beatle Paul McCartney.

- Queen Elizabeth II has reigned through the terms of 12 different British Prime Ministers: Winston Churchill (1951-55), Sir Anthony Eden (1955-57), Harold Macmillan (1957-63),

- Sir Alec Douglas-Home (1963-64), Harold Wilson (1964-70) and (1974-76), Edward Heath (1970-74), James Callaghan (1976-79), Margaret Thatcher (1979-90), John Major (1990-97), Tony Blair (1997-2007), Gordon Brown (2007-2010) and David Cameron (2010-present).