Here's the reason King Charles and Princess Diana broke from tradition and did not have their royal wedding at Westminster Abbey.

By mid-1536, Mary was the only one of the king’s subjects who had yet to accept Henry’s status as head of the church and the invalidity of his marriage to her mother, Catherine of Aragon.

Lady Mary: Henry’s daughter by Catherine of Aragon. Declared illegitimate after her parents’ marriage was annulled, she is fiercely Catholic and never stops believing she is the rightful heir.