Prince William and his bride, Kate Middleton, visited the Westminster Abbey to listen to a rehearsal of the music that will be played at their wedding.
The royal couple are scheduled to wed at the building April 29.
The Daily Express reported they were "sneaked into" the abbey via a back gate in Prince Charles' dark-blue Jaguar, and left via the same gate an hour later.
Prince Charles joined them to help them make a decision about the music.
A royal insider said: "They looked relaxed and seemed to enjoy themselves. They are obviously very keen that everything should be right on the big day."
The orchestra comprised of about a dozen young people wearing black velvet cloaks.
Another royal source said the couple's visit was to choose which music would finally be used and which they wanted to discard.