The Prince of Wales and Duchess of Cornwall shared jokes with singer Gary Barlow and comedian Michael McIntyre before a glittering drinks and dinner reception.
Charles and Camilla were greeted on arrival at the Savoy Hotel in central London by the celebrities as they attended a gala event to help raise money for The Prince's Trust.
The Take That singer, asked by Charles whether he was nervous before playing a set, said he loved performing.
McIntyre said he was not faring so well, joking with the royals: "I'm scrabbling around for things to say."
Earlier, in the hotel foyer Charles, in a tuxedo, and Camilla, wearing a navy blue Bruce Oldfield dress, met Trust-supported young people who were helping to prepare and serve the dinner.
Charles joked with one of them: "Don't spill anything."
Another Trust-supported young person, Michael Meeuwissen, had a hard act to follow. He was set make a speech after Charles to the hundreds of guests, including celebrities such as TV presenter Philip Schofield, dancer Kristina Rihanoff and boxer Joe Calzaghe.
Mr Meeuwissen, from Kettering, Northants, who has a speech impediment, also met the royals before his speech. The 26-year-old turned his life around with the help of the Trust. He had suicidal thoughts when he was as young as eight and an unstable life, which included suffering domestic violence and his mother's death when he was 11.
After turning to drugs and alcohol by the age of 12, he drifted from job to job before quitting drugs and joined a Trust Team Programme - a 12 week personal development course when he was 25, almost exactly a year ago. It was so successful that he now volunteers as a team leader on the scheme. I was telling everyone earlier I actually made a joke once when I was on the Team Programme that one day I would meet Prince Charles and I never expected that to actually come true," he said.
"But now everything has happened, it has just gone from strength to strength. It has been an incredible journey from being the kid that stuttered in school and got picked on for it, to speaking in front of hundreds of people."