To this day, Bessette-Kennedy – who died in a plane crash almost 25 years ago alongside her husband John F. Kennedy Jr – remains a source of inspiration designers; from Wes Gordon at Carolina Herrera, to Gabriela Hearst and even Ralph Lauren, who was said to ask his creatives to think of her as their muse.

You can still see her influence in brands such as Tory Burch, Khaite and Jil Sander. Sporty & Rich’s most recent advertising campaign is inspired by Carolyn and John’s paparazzi pics from the 90s. Countless articles are still published about her style. Instagram accounts abound, such as @carolynbessette – which has 54,000 followers – created by Jack Sehnert when he was an accessories designer at Steve Madden, exhaustively document her style, which has been described as everything from “effortful effortless” to “throwaway chic”.

As Sehnert once told trade publication WWD, “I started this account … as a place to create a modern homage to all that her name instantly conjures. In the years since her death, her name has almost become an adjective to describe an entire way of dressing, be it bridal or off-duty casual.”

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The thing about Carolyn Bessette-Kennedy is you’d still wear most of her outfits today. This is as true for the Yohji Yamamoto white shirt and black skirt she wore to a gala (and recently emulated by Meghan Markle, Duchess of Sussex) as it is for the beige midi-skirts and boots, the red Prada coat, the Narciso Rodriguez silk slip she wore for her 1996 wedding that changed the bridal industry forever.

She had that impossible to define “It” factor in spades. Partly because she remains mostly an enigma – dying aged 33 has left her a mystery in the era of oversharing.

The enduring fascination with Bessette-Kennedy’s style inspired London-based fashion director, writer and curator Sunita Kumar Nair to write CBK: Carolyn Bessette Kennedy: A Life in Fashion. The new book examines her style, looking at what her fashion essentials – including the shirts, the red lip, the tailoring – said about her. The book includes unseen images, and essays and interviews with designers, photographers, industry insiders and friends of Bessette Kennedy, including some from her days before “Camelot”, as the era of the presidency of John F. Kennedy, John Jr’s father, was known. Given Bassette-Kennedy didn’t court the spotlight, focusing on her fashion was important to the author.

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“Something I was very mindful of when I did the book – I knew that she was private and I knew that there was a line to be drawn. So when I did speak to close friends, it was just about the subject of fashion and how she used it to her advantage. She let the clothes do the talking,” she says from London.

One way Bessette-Kennedy did this, says Kumar Nair, was using clothes as a form of protection even while she truly loved fashion.

“[Her clothes] kind of looked like armour in a way. The way that she put it together. She would button everything up and she would belt the belts that needed belting. And I think there was a kind of protective element, but also an innate understanding of the construction of each garment she wore. She respected the designer … I think there’s just an attention to detail, which she was great at doing,” she says.

As Kumar Nair captures in the book, the picture painted by Bessette-Kennedy’s friends, former colleagues and fashion and media insiders is of a woman of innate style, fun, complexity and wit. Her grasp of what personal style really is remains compelling to Kumar Nair. Her outfits were never “simple”.

“If you’re looking at it just from an outside point of view, she’s incredibly stylish and chic, but there’s also the cleverness to the way that she had … the pieces she picked, the way she edited them, the way she made sure they fit her perfectly. I think there aren’t that many muses who do that kind of minimalism,” says Kumar Nair.

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For her it makes sense that Bessette-Kennedy remains a fashion influencer all these years later.

“I think it’s very aspirational for designers because they see a woman who looks not only beautiful but confident and carries the looks with a kind of authenticity and a sense of self. I think that’s what every designer wants. They want their customers and clients to feel these things when they’re wearing their clothes,” she says.

“I think Phoebe celebrates the intellectual woman and [Carolyn] wasn’t just beautiful, she was also super smart,” adds the author. “I think that’s something that was kind of overlooked because she was probably seen as John’s wife, but she was her own entity.”