There have been 11 presidents of the United States since the Queen came to the throne in 1952 and she has met every one of them except Lyndon B Johnson who took over after the assassination of John F Kennedy in 1963. She met another serving president before her coronation and she also met a former president during her reign.
The Queen Elizabeth II and Prince Philip meet Barack and Michelle Obama at Buckingham Palace on 1 April 2009
George W Bush winks as he and the Queen deliver speeches at the White House on 7 May 2007
Bill Clinton, accompanied by his wife Hillary and daughter Chelsea, talks to the Queen at Buckingham Palace on 14 December 2000