The Duchess of Cornwall revealed to Lady Gaga that her "grandchildren call me Gaga", as she arrived at the Royal Variety Performance.
Camilla, accompanied by the Prince of Wales, also met Robbie Williams and charity bosses before the show.
The Duchess was given flowers by the young granddaughter of Bill Kenwright, producer of the performance, before the royal couple took their seats in the Hammersmith Apollo, London.
Host and comedian David Walliams led a group of people to the royal box, asking Charles and Camilla "can I see your tickets please?", before joking to the group: "There's some riff-raff here sitting in your seats."
Gaga and Robbie will perform alongside Sting and Emeli Sande, while magician and Britain's Got Talent winner Richard Jones will also take to the stage.