Few people get the chance to work closely with the Duchess of Cambridge but British Vogue editor Alexandra Shulman was given a rare glimpse into the elusive royal's life when she shot her for the magazine - and she's shared the details of their encounter.

Kate, 34, was the cover star of Vogue for its 100th anniversary edition - the first time she had ever posed for a magazine photoshoot.

So what was it like to work with one of the world's most famous women? "She's incredibly likeable," Shulman told ES Magazine's Charlotte Edwards. "She really is. She wants to do what she's doing well, and she's very professional."

Alexandra, who has been at the helm of the fashion bible for over 20 years, also explained how she thinks Kate differs to Princess Diana.

Alexandra Shulman was given a rare glimpse into the elusive royal's life. Photo / Getty
Alexandra Shulman was given a rare glimpse into the elusive royal's life. Photo / Getty

She said: "Diana was more interested in that high-voltage celebrity, that was something she really embraced. 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."

Alexandra worked closely with Kate when she shot her for the magazine's centenary cover, which she managed to keep a secret for four months, despite being followed by a documentary crew.

In the second part of Richard Macer's fly-on-the-wall documentary, Absolutely Fashion: Inside British Vogue, which aired last month, Shulman was filmed holding a meeting with her creative director Jaime Perlman to discuss the anniversary issue front cover.

And as the pair pored over a series of white covers with graphics of "Vogue 100" on them, there was no hint that it was all an elaborate ploy to cover up the fact the royal would be covering the centenary issue.

Macer explains that he was told Shulman, 58, would make an important announcement on 28 April.

"I'm told I must not discuss this with anyone, even Alex," he said.

He admitted that his instinct was that the long-standing editor, who has been at the helm for 24 years, was going to announce her resignation.

"I can't stop thinking about this surprise announcement," he said of the longest-serving editor of British Vogue.

"Maybe she's going to tell everyone she's leaving. I think it's a surprise party for her staff to say thanks for all their hard work."

The first he knew of the Duchess posing for the magazine was on the morning of the big announcement.

He was taken to a secret location in central London and escorted down a long corridor.

"I've been speculating quite a lot about what she's going to say but the truth is, I have no clue," he said.

Finally he stepped into a room and realised he was in the main area of the National Portrait Gallery.

There was no sign of Shulman, but all became clear when he saw two portraits of the Duchess of Cambridge being hung on the wall.

Macer admitted he was impressed by how she'd managed to get the Duchess on the cover and realised his thoughts about her stepping aside were way off the mark.

"The centenary issue is selling like hot cakes and Alex is still at the top of her game.

"Far from announcing her retirement, she'd pulled off the scoop of the year," he said.

The longest-standing editor of British Vogue did admit that she'd been waking up at 3am feeling stressed as the publication of the centenary edition approached.

"I've never seemed like someone who carries stress with me," she said. "But I do."

"I feel a huge sense of responsibility to deliver. I just want to do what I think should be done."