When Twiggy arrived in New York for the first time in 1967, her American agent Barbara Stone was an experienced hand in the modeling business who thought she had seen everything.

Stone’s stable of fresh-faced blonde models included Cheryl Tiegs, Cybill Shepherd and Martha Stewart and she was skilled at placing them on magazine covers, adept at negotiating contracts with fashion houses, deft at dealing with the demands of photographers and gossip columnists, and a reliably safe pair of hands in guiding and guarding her young charges as they faced the many pitfalls that lie in wait for the young and beautiful.

Twiggy with a Snoopy hat, photographed by Bert Stern in 1967.

However, even the urbane Stone was shocked by the media frenzy that ensued when the 5ft 6in, crop-haired gamine teenager from a nondescript north London suburb hit Manhattan. Twiggy was mobbed at JFK airport and featured on the cover of The New Yorker, Life, Vogue and Newsweek. America even created a Barbie doll in her image and a fan magazine called Twiggy: Her Mod Mod Teen World.

“I can’t begin to handle the phone calls that are coming in about her,” Stone admitted at the time. “There’s been nothing like this out of England since the Beatles and the Stones. I guess it’s somehow just natural evolution that she should be the next step. The whole world wants to do a story on Twiggy, the little girl from London who’s setting the world on fire.”

Stone rode the storm and promoted Twiggy with her characteristic professionalism but the “British invasion” did not make her life easy in several ways. On another occasion, a group of scruffy young men with estuary accents turned up at one of the celebrated parties Stone and her husband Richard regularly hosted at their New York town house overlooking the East River.

Cheryl Tiegs and Ali MacGraw in 1967.

“You’re not on the list,” her husband told them. “Don’t you know who we are?” the uninvited guests said sulkily. “I don’t know and I don’t care,” he told them. A disgruntled Mick Jagger and the other members of the Rolling Stones left with their thirsts unslaked and went in search of the nearest bar.

Stone prided herself on her ability to find and groom top models, although the qualities she spotted in them were not easy to define. “It’s really unexplainable, like charisma,” she said in 1967 when she was scouting for the American TV show Model of the Year. “But I can look at a girl and instinctively know that she has that quality. It’s just something — a certain thing about certain girls. They have a spirit, a freshness that projects. It’s in the way they walk. They don’t tread. They seem to be walking on air.”

One of those she discovered for the Model of the Year show was Shepherd, who went on to have a successful acting career and starred in The Heartbreak Kid opposite Charles Grodin.

A reliably safe pair of hands in guiding and guarding her young charges as they faced the many pitfalls that lie in wait for the young and beautiful.

Tiegs, who became the face of the CoverGirl makeup range, was another who benefited from Stone’s matronly protection, which included putting up her “girls” rent-free in the family home. “I was painfully shy, and she was warm and took me under her wing,” Tiegs said.

Some of her charges were still at school, such as the 16-year-old Lucy Angle, who lived with Stone’s family. Her mentor promoted Angle as America’s answer to Twiggy and managed her finances, giving her weekly pocket money out of her earnings. Yet ultimately Angle found the regime suffocating. “If you want to see your parents, you have to ask the agency a month in advance,” she complained.

Martha Kostyra (otherwise known as Martha Stewart) in 1961, when she was a student at Barnard College, in New York City. She was named one of Glamour’s 10 best-dressed college girls.

“She ran a tight ship,” recalled Bonnie Trompeter, who was 14 when she started modeling. “We had to show up on time, with our hair done and our makeup on. There were no divas in those days.”

When Tiegs left to join the rival Ford Agency, she could not bring herself to break the news to Stone face to face and so wrote her a letter. “I knew if I saw her in person she would talk me out of it,” she said.

Although Stone operated in the Swinging Sixties she was, in the argot of the era, unashamedly “square”. She was strict about etiquette and a stickler for punctuality and despite signing a new breed of unconventional models such as Twiggy and the exotic 6ft German countess Veruschka, she gave the impression that she secretly hankered after an earlier, classically more elegant era when models wore twin sets and pearls and white gloves.

“Agents in those days were very proper,” recalled Stewart, who at the time was known as Martha Kostyra, and was paying her college tuition fees as a history student with her modeling earnings, after Stone had contracted her to Chanel.

“I remember getting a call from her telling me to iron my clothes. I was in Paris, and someone had complained because I had shown up wearing a dress that was wrinkled from the suitcase. Barbara was our mother hen.”

She is survived by Richard Stone, a magazine illustrator and painter, whom she married in 1964. She is also survived by her daughter Julie and son Lucas. An early marriage to George Frederic Pelham III ended in divorce.

Marisa Berenson in 1967.

Barbara Sue Thorbahn was born in 1933 and grew up in Swarthmore, a small but prosperous suburb of Philadelphia. Her mother, Alice (née McGinley), was a homemaker and her father, Stewart Thorbahn, was a newspaper reporter and editor.

At Swarthmore High School she was voted most likely to succeed and was a popular cheerleader. She completed her education at Gettysburg College and as the 1960s dawned was recruited by the former theatrical agent Stewart Cowley to run Stewart Models.

Stone swiftly turned it into New York’s second most important agency and the main rival to the longer-established Eileen Ford Agency, whose enviable roster of models in the 1960s and 1970s included Jean Shrimpton, Ali MacGraw, Candice Bergen, Jerry Hall and Kim Basinger. In his book Model: The Ugly Business of Beautiful Women, the author Michael Gross called the two agencies the “Hertz and Avis” of modeling.

Stone’s eagle eye sometimes enabled her to trump the rival agency, such as when she signed Marisa Berenson, whom Eileen Ford had told, “You’ll never make it as a model. You don’t have the look.” Stone spotted something Ford had failed to see and within weeks Berenson was in Paris modeling the autumn collections and being photographed by David Bailey for the cover of Vogue.

As the business changed in the mid-1970s and became more cutthroat, particularly after the arrival on the New York scene of the controversial John Casablancas and his Elite agency, Stone moved on to fresh pastures and set up a production company which made beauty films for television.

She also briefly worked as a real estate agent and in 1996 launched the literary journal, Hampton Shorts, which published short fiction by her Long Island neighbors including Joseph Heller.

Barbara Stone, modeling agent, was born on November 20, 1933. She died of congestive heart failure on April 26, 2021, aged 87