HRH Maria Walpole, The Duchess of Edinburgh & Gloucester

another source says that she was born 3 July 1736 and baptism date is 10 July 1736

Maria was born illegitimate. She married the Earl Waldegrave and had a son and two daughters by him. After his death, secretly married H.R.H. Prince William, brother to King George III. Another brother wanted to marry against the Crown's wishes. Parliament passed a Royal Marriage Act that made it illegal for Royals to marry without the Crown's permission. Since they could not back date it and Maria wed before this Act, the King was forced to acknowledge the union. However, Maria was never received at Court. Her children by him were H.R.H. though.