Queen Elizabeth II became Britain's longest-reigning monarch Wednesday, surpassing her great-great-grandmother Queen Victoria. Here are the key milestones in her life:

-April 21, 1926: Born Princess Elizabeth Alexandra Mary in Mayfair, London, the first child of the future King George VI and Queen Elizabeth, later called the Queen Mother.

-Dec. 10, 1936: Elizabeth becomes heir-apparent to the throne after King Edward VIII abdicates and her father becomes king.

-Oct. 13, 1940: Elizabeth makes first public speech at age 14 on the BBC Children's Hour to reassure children who had been separated from their parents during the Blitz.

-1945: Elizabeth is made a Subaltern in the Auxiliary Territorial Service, serving for Britain during World War II.

-Nov. 20, 1947: Elizabeth marries Prince Philip Mountbatten of Greece and Denmark at Westminster Abbey.

-Nov. 14, 1948: Prince Charles, now Prince of Wales, heir-apparent to the throne, is born.

-Aug. 15, 1950: Elizabeth's second child and only daughter, Anne, the Princess Royal, is born.

-June 2, 1953: Crowned Queen Elizabeth II at Westminster Abbey at the age of 25, upon the death of her father George VI. Many Britons bought their first television in order to watch the ceremony. The new monarch sets out on a tour of the Commonwealth, visiting places including Bermuda, Fiji, Tonga, Australia, and Gibraltar.

-Feb. 19, 1960: Elizabeth's third child, Prince Andrew, is born.

-March 10, 1964: Elizabeth's fourth child, Prince Edward, is born.

-May 1965: Elizabeth makes a historic visit to West Germany, the first German visit by a British monarch in 52 years.

-1977: Elizabeth celebrates her Silver Jubilee, which marks 25 years on the throne.

-1992: Elizabeth has what she describes as an "annus horribilis," or a "horrible year." The year sees marriages for three of her four children end. Also that year, a fire damages Windsor Castle. Public outcry over the cost of repairs amid a recession prompts the queen to volunteer to pay income taxes.

-Aug. 31, 1997: Princess Diana dies in a car crash in Paris. Under public pressure to demonstrate her grief, Elizabeth makes an unprecedented TV broadcast in tribute to Diana's memory.

-2002: Elizabeth marks 50 years of reign with her Golden Jubilee. The year also sees the deaths of Elizabeth's mother and her sister, Margaret.

-Dec. 20, 2007: Elizabeth becomes the longest-living British monarch, overtaking Victoria, who died at age 81.

-May 2011: Elizabeth makes a historic visit to Ireland - the first visit by a British monarch since Irish independence.

-2012: Elizabeth marks 60 years of her reign with a Diamond Jubilee.

-Sep. 9, 2015: Elizabeth surpasses Queen Victoria and becomes the longest-serving monarch in British history.