"Sarah, remember that yourself is good enough,” Ferguson said the Queen — whom she called, “Mumma" — said to her before she died at Balmoral Castle in Scotland. “She kne

Sarah Ferguson and Princess Diana were both sisters-in-law and friends as they navigated marrying into the Royal Family in the 1980s. And while they had their ups and downs over the years, Ferguson called Diana her "best friend" in a recent interview with the Sunday Times.