Princess Diana and Sarah Ferguson knew each other long before they married into the Royal Family—it was Diana who set Ferguson up with Andrew Mountbatten-Windsor, after all. Although they were close friends at one time, their relationship fell apart for one major reason, as royal biographer Andrew Lownie shared in a new video.

Lownie, who recently released an updated version of his book Entitled: The Rise and Fall of the House of York , told the Daily Mail that Sarah and Diana’s relationship was “a very complex one.” The women were friends from growing up in aristocratic circles, and once they were both married, Diana “would go to Sarah Ferguson every Sunday and they would moan about the Royal Family,” per Lownie.

As royal wives, they experienced similar struggles, with the author noting that they “ felt very restricted within the confines of the Royal Family.” Sarah, for one, was often called a breath of fresh air by the press during the earlier days of her relationship with Andrew, but they soon turned…