FILE - This is a Sunday April 16, 2017 file photo of Britain's Queen Elizabeth as she leaves the Easter Sunday service in Windsor Castle, in Windsor England. Britain's Queen Elizabeth celebrates her 91st birthday on Friday, April 21, 2017. (Peter Nicholls/Pool File via AP)
FILE - This is a Tuesday, April 11, 2017 file photo of Britain's Queen Elizabeth as she meets residents during a visit to Priory View, an independent living scheme for older residents, in Dunstable, England, Tuesday, April 11, 2017. Britain's Queen Elizabeth celebrates her 91st birthday on Friday, April 21, 2017.
FILE - In this Saturday, June 13, 2015 file photo, Britain's Prince William holds his son Prince George, with Queen Elizabeth II, right, Kate, Duchess of Cambridge and the Prince of Wales during the Trooping The Colour parade at Buckingham Palace, in London. Britain's Queen Elizabeth celebrates her 91st birthday on Friday, April 21, 2017
FILE - In this Nov. 20, 1947 file photo, Britain's Princess Elizabeth leaves Westminster Abbey in London, with her husband, the Duke of Edinburgh, after their wedding ceremony. Britain's Queen Elizabeth celebrates her 91st birthday on Friday, April 21, 2017.
In this 1927 file photo, Princess Elizabeth is taken for a ride in the grounds of Windsor Castle, with her cousin, the honourable Gerald Lascelles, right, son of Princess Royal. Britain's Queen Elizabeth celebrates her 91st birthday on Friday, April 21, 2017.
The Associated Press
Queen Elizabeth II, who celebrates her 91st birthday on Friday, is Britain's oldest-ever monarch and the world's longest-reigning king or queen. Here's a look at some milestones and numbers related to the queen:
— Elizabeth has reigned for 65 years and 75 days. On September 9, 2015, she became Britain's longest-reigning monarch, passing her great-great-grandmother Queen Victoria.
— She is the world's longest-reigning living monarch since the death of Thailand's King Bhumibol Adulyadej last year.
— She has had 13 British prime ministers serve during her reign, from Winston Churchill to Theresa May.
— She has met 12 U.S. presidents, from Herbert Hoover (after he left office) to Barack Obama, more than a quarter of all the U.S. presidents since Independence. She is due to host President Donald Trump for a state visit later this year.
— She has traveled more than 1 million miles (1.6 million kilometers) on official trips, visiting 106 countries.
— She has visited Canada 22 times —the largest number of trips to any nation.
— She has four children, eight grandchildren and five great-grandchildren.
— She has cut back on her official duties in the last few years, but Elizabeth still conducted 332 official engagements in 2016.