Since tying the knot to Prince William back in 2011, Kate Middleton has become a royal fashion icon stepping out in an array of stylish ensembles for her official appearances. However according to British Vogue's editor-in-chief Alexandra Shulman, the Duchess of Cambridge dressing up is her showing her "professional side."

The royal mom-of-two graced the cover of the magazine's June issue earlier this year showing off a more relaxed side to her. Alexandra noted how "incredibly likable" and "professional" the Duchess was during the shoot – as well as how different she was from her late mother-in-law, Princess Diana.

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Kate shows her "professional side" by dressing up Photo: PA

"Diana was more interested in that high-voltage celebrity, that was something she really embraced. One of the things I've learned in this job is how much celebrity is a decision," Alexandra said in an interview with ES magazine.

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She added, "The Duchess of Cambridge is prepared to do her bit, but it's not one of the things that she most cares about. She loves her kids and the countryside. Dressing up, that's a professional side to her. It's a sort of uniform, all those lovely couture costumes."

The Duchess starred on the cover of British Vogue's June issue Photo: Josh Olins

As for what it was like working with the Duchess? Alexandra revealed, "She's incredibly likable, she really is. She wants to do what she's doing well, and she's very professional. That's the point with the royal family. It's when they stop being professional that things go wrong."

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The editor noted, "We want them to be pros, to get everything right, to be on message and look great. We don't want them to have off days."

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Kate's debut on the cover of British Vogue marked the first time Prince George's mom had ever posed for a magazine. The series of portraits were released as part of a collaboration between British Vogue and the National Portrait gallery, and were added to the Vogue 100: A Century of Style exhibition.

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