‘You don’t see the other side of her and she isn’t going to tell you’ - Scott and Sarah Jessica Parker in New York in 2012

‘She had just dressed Christina Hendricks for the 2014 Academy Awards’ - Scott and Hendricks at the launch of the Banana Republic L’Wren Scott Collection in LA last November.

‘L’Wren was really at the start of her career’ - Scott with, from left, Jade Jagger, Georgia May Jagger and Mick Jagger, at the annual Serpentine Gallery Summer Party in London in 2013.

She didn't leave a note. Months after the fashion designer L'Wren Scott's suicide, this has been one of the hardest things for her friends to bear. Partly, it just seems so out of character. Those who knew her describe Scott as "thoughtful", "kind" and "sweet-natured".

She would remember birthdays or send out-of-the-blue texts saying that she was thinking of you. When she spoke, you felt you had the entirety of her attention. If she liked you, Scott would go out of her way to help.

Her friend and hairdresser, John Vial, recalls that she was always trying to introduce him to "wealthy billionaires" who would help him expand his business. "She'd send me a text saying, 'Oh my god, I saw this person, I'm introducing you to him.' Or it would be, 'I've found this new cream - try it, take it, take, take, take.' She was just a kind, thoughtful girl, really."

Simon Kneen, the former creative director at Banana Republic, who became close to Scott when he worked with her on a collaboration for the store last year, has a particular memory of a long, stressful day of photo shoots that started early and ended late. "It was actually my birthday," he says. "And, when I got home, there was this beautiful bouquet of peonies she'd arranged to be sent to my apartment."

At her memorial service in New York in May, Scott's brother, Randall, spoke of her "deep heart, especially for the underdog". As a child, he said, she became firm friends with a neighbourhood child with Down syndrome. Her school friend, Julie Nichols Thompson, remembers Scott as a teenager being "tall, dark and slender. I was chubby and blonde. She didn't care and she never made me feel bad about myself . . . She would occasionally say, 'Jules, what's wrong with your hair today? Let me help you with that.' At that age, she could easily have made fun of me."

Her talent, says Joanna Coles, the editor-in-chief of Cosmopolitan in the US, "was that she made people feel special. She seemed warm and funny, and sort of sympathetic. She would put a hand on your shoulder or an arm around you. Women loved her and responded to her. She was a girl's girl."

"She gave an impression of a certain serenity," agrees the respected fashion critic, Suzy Menkes, "which is so out of tune with her sad death."

In an industry renowned for its superficiality and occasional bitchiness, for its hectic pace and consumer-driven culture, Scott's calmness and consideration for other people set her apart.

She didn't need to care - at 49, she was glamorous, successful and had a superstar boyfriend in the form of Mick Jagger. Her red-carpet gowns, known for their classic tailoring and sumptuous detailing, were worn by Hollywood A-listers including Sarah Jessica Parker, Nicole Kidman and Renee Zellweger, and Scott had just dressed Christina Hendricks for the 2014 Academy Awards.

Although her business was accumulating debt, she was, to all intents and purposes, wealthy. She owned her $5.6m New York apartment on 11th Avenue outright, having paid off the $1.25m mortgage last year. Scott also had homes in Paris and London, which she shared with Jagger. Their Paris flat contained a bathroom lined in Lalique glass.

All of which suggests a certain lifestyle, played out at a remove from the everyday. But, says Kneen, "She was never a diva. She was a great listener and interested in everyone, from pattern-makers through to seamstresses and designers . . . She wasn't pretentious. My team used to love working with her."

So it seems odd that Scott would choose such a brutal way to end her life. Odd, too, that she would text her assistant, Brittany Penebre, at 8.30 on the morning of her death, asking her to come round. It was Monday March 17 and, by the time Penebre got to the apartment at 10am, Scott was dead. She was found fully clothed, her 6ft 3in frame slumped on the floor, having hanged herself with a black silk scarf.

Penebre called for an ambulance, but the paramedics were unable to do anything. Later, Scott's body was removed from the building for autopsy - the blue and white medical examiner's van nudging its way through a gathering crowd of photographers.

As news of her death spread, Scott's friends were left reeling. No one had anticipated it. She had just returned from a holiday in Mustique. The night before her death, she'd held a dinner party for close friends. They were concerned about her - she seemed down, slightly troubled, perhaps - but there was no sign of what was going to happen, just hours later, in the same apartment.

The day after her death, Jagger, who was on tour with the Rolling Stones in Australia, issued a statement claiming he was "still struggling to understand how my lover and best friend could end her life in this tragic way".

Some seized on financial problems as the most likely reason for her death. The UK arm of her company, LS Fashion Ltd (set up in 2006), had a deficit of £3.5m, and she had cancelled her show at London Fashion Week in February, citing production delays. Although she dressed many celebrities at red-carpet events, it is unlikely they paid for the privilege. Sales were hard to come by: Scott's clothes were expensive investment pieces and beyond the price range of all but the super-rich.

The New York Times fashion critic, Cathy Horyn, claimed Scott was demoralised by the difficulties besetting her business and had been planning to close it down - a claim denied by Scott's spokesperson, who said that, at the time of her death, "the long-term prospects for the business were encouraging", in part due to the designer's expanding portfolio of brand partnerships, with Banana Republic and the cosmetics firm, Bobbi Brown, among others.

Kneen insists that the debts were not particularly significant for that kind of start-up. Scott, he says, was "really at the start of her career".

Besides, if she genuinely were in financial crisis, there were always going to be people who would bail her out - not least Jagger himself. The debt, such as it was, didn't seem enough of a reason for Scott to take her own life.

"I just don't know why she would do it," says Vial, shaking his head. "I could not be any more shocked. I had no inkling at all. None, none, none."

The only way he can make sense of it is to think that it was an impulsive act. "I just don't think she meant to do it," he says, and there is a helplessness to his tone, an underlying desperation to eke out some kind of unhappy logic from the mess. "It was a moment of madness. I don't think she knew . . ." He trails off.

It's the thing they all keep coming back to: the strangeness of it, the fact that Scott - so compassionate, so kind, so seemingly serene - had texted her assistant without imagining the trauma of the discovery that would await her, without worrying about the effect it might have. It was so out of character. All of it. And there was no note to explain why.

In his book, The Savage God: A Study of Suicide, the writer, Al Alvarez, argues that "the decision to take your own life is as vast and complex and mysterious as life itself".

In the case of L'Wren Scott, the mystery of her death is heightened by a deeper unknowability. For all that she was loving and loved, admiring and admired, her friends were aware there were things she chose not to share. She was extremely private and adept at putting up a front.

Her estranged adoptive sister, Jan Shane, described Scott in a recent newspaper interview as "a super-strong woman . . . [You] don't see the other side of her and she isn't going to tell you."

She had a "guarded core", wrote Bridget Foley, the executive editor of Women's Wear Daily in the aftermath of Scott's death. Sarah Jessica Parker recalled at Scott's memorial service at St Bartholomew's Church on Park Avenue that there was a mysteriousness to her which was hard to pin down, marked by "silent boundaries" her friends would know not to cross. Occasionally, this distance could be interpreted as froideur.

"Her strongest tool was the power of silence," says Vial. "Even if she wasn't angry, she just said things with a sense of authority."

And there was the extraordinary physical presence, too - Scott was well over 6ft in her bare feet, with waist-length dark hair and the languid elegance of a ballerina.

She didn't feel the need to ingratiate herself and wasn't especially impressed by the trappings of fame. She had a dry, ironic sense of humour, much given to an arched eyebrow and a sarcastic one-liner.

When she first met Jagger, on a 2001 photo shoot, she had little knowledge of his back catalogue. Later, when they were dating, they attended a fashion show in Paris, where the models walked down the catwalk to a series of Rolling Stones hits. It took Scott three goes to successfully identify Gimme Shelter. She was her own woman, then, and uninterested in being known purely as a rock 'n' roll appendage.

There were some who took exception to what they perceived as her coldness. Keith Richards was rumoured to call her "Le Man" and to tease her about the size of her feet. There were others who referred to her dismissively as "the apostrophe", and complained that she exercised too great an influence over Jagger's decisions. He was, they say, more reserved and less fun when Scott was present.

Her perfectionism could make her controlling. When she designed Jagger's on-stage outfits, Scott ripped up 25 pairs of jeans before she was satisfied with the final version. When she renovated the couple's Left Bank apartment in Paris, she took nine months choosing the paint for the drawing room, evaluating what shade looked best in various lights, weathers and seasons (in the end, she opted for four subtly different shades of grey).

But those who knew her insist the standards she set herself sprang from an innate insecurity. This, after all, was a woman who had been given up for adoption at birth. However happy Scott's subsequent upbringing might have been, some people in that situation have a hard time getting over the initial rejection and feel a constant need to prove their worth.

Perfectionism is a common ailment, too, among successful women. For some, the exhausting business of never feeling quite enough is appeased by motherhood. Although Scott never talked about having children, or the unsubstantiated rumours that Jagger was incapable of long-term fidelity, some of her circle believed that she wanted a baby. Jagger has seven children by four different women and four grandchildren. His first great-grandchild was born in May.

Scott was, by all accounts, an attentive and loving presence in their lives. She took pride in the children's achievements, telling friends when Georgia May, Jagger's model daughter, had a new magazine cover out and attending his grandson Zak's first baseball game in the months before she died. The eight-year-old Zak called Scott "Glammy" - an affectionate contraction of "glamour" and "Granny".

Menkes recalls that Scott had a "very good, easy relationship" with Jagger's children - "not motherly, just natural". But there were signs that Scott wanted more.

"There were two times, the whole time that I knew her, when I saw . . . I wouldn't say the mask slipping, but, perhaps, a bit of what was actually behind her," says one close friend.

"One was when she showed me around her Paris flat five or so years ago. She had some rooms off the corridor she was in the middle of doing up and she said, 'Of course, that will be for the children.' I said, 'Oh, do they often come to stay?', thinking she meant Mick's children, and she gave me a quizzical look and said, 'Well, we never know, do we?' And I felt . . . it's hard to say, but I felt I'd made a blunder.

"The second time was at her Ile Saint-Louis showroom three years ago. She seemed very depressed and unlike herself, quite insecure and generally upset. I was so worried about her I actually asked a mutual friend, 'Is she OK?' and they said it was probably just Mick playing up again. These are the only obvious things I remember as signs that she wasn't jogging on happily with her life."

It says something about how cautiously Scott guarded her private life that among her friends there is no consensus over whether she and Jagger had split up or not. I am told with equal certainty that they "definitely had called time on their relationship" a few weeks before her death and, from different sources, that any suggestion they were no longer a couple is "100pc false".

Jagger's spokesman, Bernard Doherty, has openly dismissed rumours of a split as "absurd". However, stories have recently emerged of Jagger becoming close to a 27-year-old ballet dancer, Melanie Hamrick, whom he is said to have met while on tour in Japan, several days before Scott was found dead. In spite of this, one of Scott's confidantes insists that the notion of a split was "truly unbelievable. I would be less shocked if the Pope decided to be a Muslim. They were great together.

"They were like kids. She would light up any time he walked into a room. It was like, ting!" In many ways, the friend continues, it would be preferable if there had been a rupture "because at least it would be an explanation, wouldn't it?"

If she was depressed, Scott managed to hide it from most people. And the truth was that, even if Scott could have made sense of what she was feeling, she might not have wanted to share it with anyone. It was that "guarded core" which drew her to fashion in the first place.

Her clothes reflected this aspect of her personality: beautifully constructed to flatter the wearer, but always concealing more than they revealed. Each carefully crafted piece required an enormous amount of work and attention to detail in order to maintain the illusion of grace. They were one-offs. And so, in her own way, was L'Wren Scott.

She was raised Luann Bambrough in Roy, Utah, a city with a population of 37,000 situated alongside Interstate 15. Scott's adoptive father, Ivan, was a World War II veteran, who worked as an account executive for an insurance company, and her mother, Lula, was a bank clerk. Both were active in the Church of the Latter-day Saints. Scott's siblings - Jan and Randall - were also adopted, and all three went to the local high school.

It was a modest upbringing and Scott soon outgrew her surroundings. At the age of 12, she was already 6ft and towering above her 5ft 1in mother. At the cinema, she would be charged more for a ticket because the ushers didn't believe she was a child. "She was frequently made fun of because of her height," recalls her childhood friend, Julie Nichols Thompson. "She seemed to take it in her stride. I wouldn't say she was maliciously bullied, but she was often called Stretch or asked, 'How's the weather up there?'"

Her height meant that store-bought clothes didn't fit. Her mother encouraged her to start adapting Butterick patterns and remodelling men's suits for her frame.

"She loved her mum," says Vial. "Her mother used to say to her, 'Stand up straight, shoulders back, get your heels on!' She was very close to her mother, I think.

"Certainly, there was no taboo. I don't think that she had any issues about being adopted. She never vocalised them to me."

Nichols Thompson says the only time it came up was when peers would ask whether Scott had tall parents. "She loved and respected her [adoptive] parents," she says. "Confidence was one of her great attributes."

Scott was funny and outgoing, with a diverse group of friends. She made no secret of the fact that she believed her future lay beyond Utah and used to carry a sketchpad of drawings under her arm around school. "The local swimming pool was across from my house. We met our friends there nearly every day during the summer," says Nichols Thompson. "We were constantly trying to get the attention of the lifeguards by pretending to be attacked by a shark, feigning drowning, or 'accidentally' splashing them.

"We would position ourselves right under the lifeguard chair and hang our elbows over the edge of the pool with our legs extended and begin kicking to see how wet we could get the lifeguard before he reprimanded us. L'Wren's legs were most efficient in creating a splash zone.

"One time, we were piling into the back of a two-door Chevy. As the young man tipped the driver's seat forward to let us in, L'Wren looked at the small space and then offered to unscrew her legs and put them in the trunk."

In 1985, when she was 18, Scott was spotted by the legendary photographer, Bruce Weber, on a trip to Utah. He later shot her for a Calvin Klein commercial, for which she was given $1,500. She moved to Paris, where her agency renamed her L'Wren. Although she was deemed too tall for regular catwalk shows, her 42in legs got her a lot of work.

She was featured in an iconic advertisement for Pretty Polly hosiery, shot by David Bailey, where her legs were pictured as the hands of a clock.

"We saw thousands of girls," Bailey recalls, "and she had the best legs in the world. It was a difficult job because I was 30ft up in the sky shooting down on her, and she didn't complain once. I was surprised when she died. She seemed quite together to me."

In the mid 90s, Scott moved to Los Angeles and began to work as a stylist for photographers including Herb Ritts, Helmut Newton and Mario Sorrenti. Her shoots were featured in Vanity Fair and W magazine.

There was a brief marriage in 1993 to property entrepreneur Anthony Brand, but the couple divorced after three years. In 2001, she met Jagger on a photo shoot. Five years later, with his support, she set up her own label.

Her trips back to Utah became less frequent, particularly after her parents died (her father in 2002, her mother six years later at the age of 83) and her career as a designer took off. After working so hard to make her own way in life, it was said to be a cause of frustration to her that she was repeatedly referred to as "Mick Jagger's girlfriend".

"I would think she'd be pretty fed up by the 'Mick's girlfriend' tag, but that's just a guess," says Menkes. "I never heard her say anything against Mick, ever."

It was clear that she adored him. Her modelling days left her with an instinctive understanding of silhouette and, in most of the photographs that survive of them as a couple, Scott is bending gracefully at the knee to distract attention from the obvious height difference. She took joy, say friends, in making things beautiful. In many ways, she was her own most brilliant creation.

"I never saw her shabby or in tracksuit bottoms," laughs Vial. Her fashion shows were, he says, "beyond chic". Scott would always provide a lunch for her attendees, serving baked potatoes with caviar or chicken pot pie. The attention to detail was staggering: vast bowls of roses, individual waiters for each guest and, of course, the tantalising prospect of Jagger being in attendance. But, for all the stunning surface detail of her life, and the sense she gave of being in control and gilded, and lucky, Scott had an underlying fragility.

"She would be really hurt if somebody said something unkind," adds Vial. "Like many powerful women, she was sensitive."

In the months before her death, Scott's emotional fragility was matched for the first time by a physical frailty. She underwent an operation to repair a torn meniscus in her knee. For weeks, she was hobbling around on crutches.

"I think it was the first time she felt her body was giving up on her," says an acquaintance. "She was due to turn 50 in April, which could also have been playing on her mind."

Still, she carried on working. She kept in touch with friends. She emailed Andre Leon Talley on January 4 saying she'd just dropped off "my grandson, Zak" at the airport to fly back to Los Angeles. A few weeks later, she spoke to Cathy Horyn on the phone.

According to Horyn, she sounded "rundown and discouraged" and spoke of the production problems that had forced her to cancel her London show. On February 3, she texted Vial, apologising for not having been in touch sooner and complaining of "a horrid sinus virus". She signed off, "Hope to catch you soon xx."

It was the last communication he ever had with her.

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