On August 28, 1996 Prince Charles and Princess Diana divorced. As part of the agreement, Diana lost the title of “Her Royal Highness” but retained the title of Princess of Wales.
Here 2 items about the divorce from the pages of the Scranton Times.
A Royal Wedding – http://timestribuneblogs.com/pages-from-the-past/a-royal-wedding/
Death of a Princess – http://timestribuneblogs.com/pages-from-the-past/death-of-a-princess/