Olivia Palermo swears she sometimes wears sweatpants

It is a bracing winter afternoon in Manhattan, and the sun is already setting. Up on the 13th floor of a towering studio complex, I have an uninterrupted view over the mighty Hudson River, to New Jersey beyond and the sky above it, which is currently a swirling ripple of pink, orange and yellow.

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In the studio next door, a fashion shoot is taking place, but such is the security surrounding it that I’m not permitted to observe proceedings, even from a distance.

The subject is not a supermodel or a Hollywood A-lister – though she has starred in campaigns for brands including Salvatore Ferragamo, Rochas and Tommy Hilfiger, and graced myriad magazine covers – and the garments in which she is being photographed are not couture gowns or cutting-edge catwalk collections.

The combination of the woman and what she’s wearing, however – Olivia Palermo, sporting 10 outfits from the new collection by the UK brand Coast for its advertising campaign – does represent something of a coup. The 31-year-old socialite, businesswoman, brand ambassador and all-round style icon is one of the most frequently photographed women in fashion.

Front row at every major show and high on every magazine’s best-dressed list, with 4.7 million Instagram followers, she is considered the ultimate arbiter of sartorial taste.

And, renowned for mixing designer labels and mass-market items, she can influence consumers – and shift high-street stock – more efficiently than any fashion editor. If Palermo is snapped wearing a particular coat, dress, blouse or pair of boots, it’s a race against the clock to bag one before it sells out online.

A few days later, on an equally brisk Monday morning, I meet Palermo for coffee in Dumbo, the well-heeled waterfront district of Brooklyn where she lives with her husband of 2?? years, German model Johannes Huebl, and their Maltese terrier, Mr Butler.

She arrives looking – of course – impeccably groomed, the picture of off-duty glamour. Significantly shorter than the average model at just 168 centimetres, she is sparrow-like in her slimness, with sleek, honey-blonde hair. Even at 11am, her big brown eyes are perfectly made-up, with dusky shadow and immaculate lashes. But if anyone in the coffee shop recognises her, they are too polite to make it obvious.

She tells me she’s had a few days off – unusual, for Palermo is a paragon of industry and focus. “I probably work every day, in some way,” she says. “I like to be productive, and for us New Yorkers, it’s very hard to switch off .”

The digital centrepiece of her daily duties, and of her personal brand, is her blog and website, oliviapalermo苏州美甲学校. It publishes runway reports along with beauty and lifestyle tips, and also serves as an online store, stamped with the Palermo seal of approval. Th e website has a tiny team (“I don’t like too many cooks in the kitchen”), made up of OP, as she is known; her editorial director, Jillian Magenheim; her brother, Grant, 29, a former investment banker who now serves as her business director; and two full-time writers.

But Palermo has also built the business through strategic alliances. Along with her role as the face of Coast, she’s an ambassador for the US clothing chain Banana Republic, has a long-standing partnership with Max & Co, the contemporary offshoot of Italian fashion powerhouse Max Mara, and has spent the past year designing four seasonal collections for Nordstrom, the American chain of luxury department stores. Does she not, I wonder, feel compelled to launch her own label?

“There are so many different aspects of the industry and it’s very important to understand how each one of these companies works, so I can understand and do my job better,” she demurs. “I’m sure it will happen at some point, but I think you should always be learning.”

The daughter of a millionaire realestate developer, Douglas Palermo, and Lyn Hutchings, an interior designer, who divorced when she was a child, Palermo grew up dividing her time between Greenwich, Connecticut, where her father lived, and Manhattan’s old-money Upper East Side, with her mother. Early in her career, she was dubbed the “real-life Gossip Girl”, after the television series set in the area. (Cecily von Ziegesar, who wrote the books on which the series was based, attended the same elite all-girls school as Palermo.)

Hutchings trained her daughter in the practice of fortnightly manicures, and Palermo credits her as a major style inspiration. “I’m sure there’s something in the bloodline,” Palermo says. “I definitely get my sense of style from my mother. Sometimes she’ll call me and we’ll have worn exactly the same outfit that day. My love of blazers and jackets comes from her – she has a beautiful collection.”

Though she is a fan of chain stores like Zara and Topshop, today she’s dressed head to toe in designer labels. There are flat black ankle boots by Isabel Marant, jeans by J Brand. Her “coatigan” is by Italian luxury brand Agnona, and her highly covetable handbag by another Italian label, Analeena. She doesn’t plan outfits in advance, though. “I don’t have the time,” she insists.

A keen equestrian as a child, Palermo was also a lacrosse player, and a figure skater, and – somewhat incongruously for one so dainty – played ice hockey, too. In fact, as a teenager, she was all set to pursue a career in sports commentating.

She enrolled in a media-studies degree at the New School in New York, and spent a year at the American University of Paris, where, at 19, she says her interests “just shifted” towards fashion.

On her return, society photographer Patrick McMullan spotted her at an auction and began taking pictures of her at parties and galas. At 20, she was already being offered front-row seats at fashion-week shows. Was she at all intimidated, sharing such hallowed benches with the likes of Anna Wintour? “No, it was great – any girl would love to go to a fashion show and take in all the beautiful clothes,” she gushes.

At 22, she joined the cast of The City, a “structured reality” (i.e. staged) spin-off from the MTV series The Hills, which followed the lives of its cast members in New York. In it, Palermo worked in the PR department for fashion designer Diane von Furstenberg, then at elle苏州美甲学校, and was paid a reported $US12,000 for each episode. Though the exposure undoubtedly launched her global career, she seems eager to put the series behind her. “It was a good learning experience, but I’m happy to move on to other experiences that are in fashion only,” she says, diplomatically.

Palermo and Hanover-born, Dublin-educated Huebl, 39 – alongside whom she has modelled for brands including Tommy Hilfiger and Mango – met through mutual friends almost 10 years ago and married in June 2014 in a lowkey, intimate ceremony in upstate New York. Palermo wore a custom-made Carolina Herrera outfit.

The couple will ski in the French alpine resort of Courchevel this winter, as usual. In summer, they play tennis. She also works out with Tracy Anderson (who famously trains Gwyneth Paltrow, and formerly Madonna) six days a week. “I’m very dedicated,” she adds.

You won’t catch her getting papped in an old tracksuit exiting the gym, though. “My mother taught me at a very young age to look your best at all times,” she says. “So I have great workout and after-workout gear.”

Does she ever wear sweatpants? “Of course,” she claims. “I don’t sit at home in high heels and a ball gown. It’s important to unwind and feel comfy.”

Unwinding at home doesn’t sound a very regular event, however. “I’m home 160, maybe 170 days out of the year,” Palermo says. She spends a lot of time in London and Hamburg, where PMA, the modelling agency to which she and Huebl are signed, is based. “I love travelling; I feel most productive on the road,” she explains. She doesn’t sleep on planes, spending transatlantic flying time working instead.

Perhaps inevitably, given his upbringing, even her dog Mr Butler has launched a modelling career – he featured in an Amazon ad, helping Palermo choose Christmas presents for her friends and family. “He was the star of the show,” she beams.

Having spent her 20s growing her personal style into a global brand, and being a person who thinks long-term, Palermo must, I suggest, have a game plan for her 30s.

“I do,” she says. “But I can’t tell you, because that would defeat the purpose of my plan.” And, with a swish of a mohair sleeve, she heads off to continue building her perfectly polished empire.