Prince Philip supported Princess Diana during her rocky marriage to Prince Charles, author says

Princess Diana initially had a warm relationship with Prince Philip, another "outsider" who joined the British royal family.

In 1981, Diana married Prince Charles, the heir to the British throne. "Philip spent seven decades walking behind the queen both literally and metaphorically – but he was the backbone of the royals’ private life, supporting Diana during her most difficult periods," British author Tom Quinn told Fox News. "He also admonished his sons, including Prince Charles, when he felt their behavior was not good enough." Quinn previously wrote a book titled "Kensington Palace: An Intimate Memoir from Queen Mary to Meghan Markle" where he spoke to those who worked for the royals over the years.