Ingrid Seward detailed Princess Diana's relationships with the former Prince Charles, Prince Andrew and Prince Edward. The Princess of Wales died in 1997 at age 36.
It is believed that U.S. President Ronald Reagan was one of Britain's Queen Elizabeth II's favorite presidents. The former actor died in 2004 at age 93.
Kate Middleton revealed her cancer diagnosis in a video message in a new era of royal transparency. Here's a look at other royals who have publicly and privately battled the disease.