On July 29, 1981, the biggest royal wedding of the century was unfolding at St. Paul's Cathedral in London: future King, known then as Prince Charles, was preparing to marry then-Diana Spencer and make her the Princess of Wales, finally settling down with a wife after much urging from the royal family. We now know from Princess Diana's later recollections that her wedding day was filled with doubts and fears, as she'd already come to suspect her soon-to-be husband was involved with Camilla…