Queen Elizabeth II has reigned longer, visited more places, and met more people than any British monarch. Now she's marking a milestone of a more personal kind, Her Majesty's 90th birthday. "Downton Abbey" star Elizabeth McGovern narrates this unprecedented look into the life of perhaps the most famous woman in the world. We look back on her remarkable 63-year rule, and gain intimate insights from Prince Charles, the Prince of Wales, Prince William, Duke of Cambridge, and other members of the Royal Family.