As of tomorrow (Wednesday), Queen Elizabeth II will be the longest-reigning monarch in UK history. The previous record was set by her great-great-grandmother, Queen Victoria.
When Elizabeth was first crowned queen, 63 years, seven months and two days ago, Winston Churchill was still the Prime Minister, while Joseph Stalin ruled Russia. Current Prime Minister David Cameron had not yet been born.
Officials at Buckingham Palace say that there will not be a large event to celebrate tomorrow's achievement. Instead it will be "business as usual."