Britain's Prince William, Duke of Cambridge, and Catherine, Duchess of Cambridge, arrive at the Royal Variety Performance in London. Pictures: Reuters

London - The Duchess of Cambridge looked anything but straight-laced on Monday night as she attended the Royal Variety Performance in a daring Alexander McQueen evening gown.

Wearing her hair loose, Kate radiated glamour in the black lace overlay dress, which had a scooped back and sweetheart neckline.

She and her husband Prince William met performers, including the cast of West End musical Mary Poppins, before the show at the London Palladium.

Veteran singer and actress Petula Clark, who plays the Bird Lady, told Kate she would have to bring the children to see Mary Poppins, which has just opened at the Prince Edward Theatre.

"They would love it," the duchess said, while William exclaimed: "I love Mary Poppins!"

Kate said her children had been really excited about where she and William were going – particularly the dancing and singing – and asked if they could come. But she had to tell them: "Not on a school night!"

The evening featured performances by Lewis Capaldi, Mabel, Robbie Williams and Emeli Sande, although headline act Sir Rod Stewart had to pull out on Monday on doctor’s orders with a throat infection.

"I’m very disappointed that I can’t be there to give my support," he said on Twitter.

The show was co-hosted by comedians Rob Beckett and Romesh Ranganathan, who introduced Kate and William, teasing the couple that they were on a "date night" as the camera focused on them laughing and giggling in the Royal Box, William nodding with mock seriousness.

The event is in aid of the Royal Variety Charity, of which the queen is patron, and raises around £850 000 (about R16.3-million) each year to support elderly, sick or impoverished entertainers who need help.

Daily Mail