Queen Elizabeth II – who turned 90 on 21 April –
has met 10 serving Presidents of the United States during her reign. She didn't meet Lyndon B Johnson, who took over as President after the assassination of John F Kennedy, but she has met all of the others , from Eisenhower to Obama.
IBTimesUK takes a look at some of the Queen's encounters with US Presidents over the past 63 years.
1957: From left: Queen Elizabeth II, Dr. Elson, Former US President Dwight D Eisenhower, Former First Lady Mamie Eisenhower, Associate Minister John Edwards and Prince Philip
National Presbyterian Church
1961: From left: Prince Philip, Former First Lady Jacqueline Kennedy Onassis, Queen Elizabeth II and Former US President John F. Kennedy at Buckingham Palace
John F. Kennedy Presidential Library and Museum
1969: Former US President Richard M. Nixon, Queen Elizabeth II, Prince Phillip, Princess Anne, Prince Charles
Oliver F. Atkins
1976: Former US President Gerald Ford dancing with Queen Elizabeth II during a State Dinner held in her honour
Gerald R. Ford Presidential Library
1977: From left: Pierre Trudeau, (Prince Charles far background), Princess Margaret, Takeo Fukuda, James Callaghan, Giscard d'Estaing, Queen Elizabeth II, Prince Philip, Queen Elizabeth The Queen Mother, Former US President Jimmy Carter, Giulio Andreotti, Helmut Schmidt
Jimmy Carter Library
1982: Former US President Ronald Reagan and Queen Elizabeth II horseriding at Windsor Castle. Reagan is riding Centennial and the Queen is on Burmese.
Ronald Reagan Library
1991: Former US President George Bush talks to Great Britain's Queen Elizabeth II during a welcoming ceremony at the White House, Washington, DC, where the queen was given a red carpet welcome and a 21-gun salute
Jerome Delay/ AFP
1994: Former US President Bill Clinton and Britain's Queen Elizabeth II smile for the cameras during the group photo session at the Guildhall 04 June prior to a celebratory banquet for the 50th anniversary of the D-Day invasion of Normandy
Gerry Penny/ AFP
2003: Former US President George W. Bush was welcomed to the United Kingdom by Queen Elizabeth II and Prime Minister Tony Blair, amid tight security at Buckingham Palace
Kirsty Wigglesworth/ AFP
On 22 April 2016, the Queen met with US President Barack Obama at Windsor Castle. Accompanied by Prince Philip and First Lady Michelle Obama, the four attended a private lunch held on the castle grounds. The lunch comes as Obama pleas with the country to remain in the European Union.
2016: Queen Elizabeth II and Prince Philip, Duke of Edinburgh stand with US President Barack Obama and First Lady of the United States, Michelle Obama in the Oak Room at Windsor Castle ahead of a private lunch hosted by the Queen
John Stillwell/ Getty Images