The thigh-skimming hemline said it all. Tuesday night's pop concert with Gary Barlow entertaining, was as close to a night off as the Duchess of Cambridge gets in her hectic schedule.
Keen to let her hair down, Kate stepped out in a Zara dress which was, for her classic tastes, a daring change.
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And, in a departure from her last public appearance, when Kate wore a £1,400 Mulberry dress, the mini cost only £69.99.
Inside the venue, the Duchess and husband Prince William, along with the Prince of Wales and the Duchess of Cornwall, were treated to a rousing performance by Take That star Gary.
The star told them: "I do hope you enjoy tonight and I hope it's not too loud for you", to which fun-loving William replied: “the louder the better”.
Meanwhile, pop royalty Madonna has given her seal of approval to Kate's wardrobe choices.
"She is a lovely girl with a great sense of style" she told People magazine.
"I like her choices. She's elegant and still knows how to have some fun. I'm a fan of her style".