Twenty-year-old Diana became Princess of Wales when she married the Prince of Wales on 29 July 1981 at St Paul's Cathedral , which offered more seating than Westminster Abbey , which was generally used for royal nuptials.   The service was widely described as a "fairytale wedding" and was watched by a global television audience of 750 million people while 600,000 spectators lined the streets to catch a glimpse of the couple en route to the ceremony.   At the altar, Diana accidentally reversed the order of Charles's first two names, saying "Philip Charles" Arthur George instead.  She did not say that she would "obey" him; that traditional vow was left out at the couple's request, which caused some comment at the time.  Diana wore a dress valued at £9,000 with a 25-foot (-metre) train.  Music and songs used during the wedding included the " Prince of Denmark's March ", " I Vow to Thee, My Country ", " Pomp and Circumstance ", and " God Save the Queen ".