Task: Question Generation
Input (English): The Queen surpassed her great-great-grandmother, Queen Victoria, to become the longest-lived British monarch in December 2007, and the longest-reigning British monarch on 9 September 2015. She was celebrated in Canada as the "longest-reigning sovereign in Canada's modern era". (King Louis XIV of France reigned over part of Canada for longer.) She is the longest-reigning queen regnant in history, the world's oldest reigning monarch and second-longest-serving current head of state after King Bhumibol Adulyadej of Thailand.
Output (English): When did Elizabeth become the longest reigning monarch?