Queen Elizabeth took the throne at the age 25, and stayed there through seven decades, 15 British prime ministers and the longest reign in U.K. history. From the earliest days as Queen, Elizabeth grappled with the British Empire transforming into a Commonwealth with more self-determined nations. But in more recent years, the Queen also ruled through the death of Princess Diana, numerous royal family scandals, and political upheaval like Brexit. Today, royal historian Carolyn Harris gives us a look back at how the Queen dealt with a colonial legacy, and a look forward at how the monarchy could change without her.