No, Diana, Princess of Wales, did not have another child besides her two sons, Prince William and Prince Harry.
Diana married Prince Charles in 1981, and they had their first son, William, in 1982. Their second son, Harry, was born in 1984. The couple divorced in 1996, and Diana tragically passed away in a car accident in 1997.
While Diana's life and legacy continue to fascinate the public, there is no evidence to suggest she had any other children besides William and Harry.
