Who became the longest-reigning British monarch in 2015?

Queen Elizabeth II became the longest-reigning monarch in British history on 9 September 2015 when she surpassed the reign of her great-great-grandmother Queen Victoria. On 6 February 2017, she became the first British monarch to celebrate a Sapphire Jubilee, commemorating 65 years on the throne. On 6 February 2022, Elizabeth II became the first British monarch to reign for 70 years, and large-scale celebrations for her Platinum Jubilee occurred from 2 to 5 June. Later that year, Elizabeth II died at the age of 96, after reigning for 70 years and 214 days.

Source: Wikipedia