September 9, 2015 marks a milestone in British history as Queen Elizabeth II surpasses her great-great-grandmother, Queen Victoria, as Britain’s longest reigning monarch. Queen Elizabeth II succeeded her father, King George VI, when he died on February 6, 1952. She was twenty-five years old at the time. Queen Victoria’s reign lasted 63 years, 212 days (June 20, 1837-January 22, 1901). The Queen has remained a steadfast symbol of stability during a reign marked by tremendous changes. Photos by Getty Images.