The royal couple walked the red carpet and greeted performer Jessie J, Peter Fincham, ITV's director of television, and trustees from EABF, before entering the London Palladium for the annual event of the best of British.
But as they entered took their seats, Camilla appeared speechless as Dame Edna Everage turned up in the royal box.
The audience laughed as Dame Edna looked at her ticket and joked: "I'm so sorry, they found me a better seat".
The Royal Variety Performance, now in its 101st year, takes place in aid of the Entertainment Artistes' Benevolent Fund (EABF).
Warming up the crowd host John Bishop joked: "Be merry, be happy and no-one be beheaded.
"Obviously if mad Harry was here it would be a different story."
Bishop welcomed Charles and Camilla, congratulating them on their new grandson, but warning: "Enjoy this because soon you will be babysitting."
The Duchess, who wore a Vivienne Westwood dress in petrol blue, watched on as the evening was kicked off with a lively performance by Gary Barlow singing Greatest Day and Let Me Go.
Figure skaters Jayne Torvill and Christopher Dean took to the stage in matching purple outfits, before hip-hop duo Rizzle Kicks performed and Harry Hill treated the audience to a preview of his upcoming West End spoof X Factor musical I Can't Sing!
Making her Royal Variety debut, singer-songwriter Jessie J performed her latest single Thunder. Irish comedian Jason Byrne appeared on stage in underwear and a white vest but donned a suit jacket and bow tie to give his show.
US Grammy award winner Mary J Blige sang My Favourite Things from the Sound of Music, against a backdrop of white trees shrouded in fairy lights.
Olly Murs performed a surprise duet with Robbie Williams, singing the Jungle Book classic tune I Wanna Be Like You.
The last time the Prince and Duchess attended the Royal Variety in 2010 a protester campaigning against the rise in tuition fees attacked their Rolls-Royce limousine.
David Walliams hosted last year's 100th anniversary show in front of the Queen at London's Royal Albert Hall.