Two months ago the New York fashion world tomtoms signaled, "Watch her!" It has, and by now the opinion is nearly unanimous. She's the new girl in town, the fall sensation, as fresh as a breeze of western mountain air. She is tall and rangy—"all of 5'12"," she says—a lightened blond with cornflower blue eyes, uncapped teeth and dimples that go on forever. She is Margaux Hemingway—and, yes, she is that Hemingway, granddaughter of novelist Ernest "Papa" Hemingway and daughter of Jack, stockbroker turned Idaho fish and game commissioner (PEOPLE, Sept. 2).

It has all happened so quickly that even 19-year-old Margaux can hardly believe her luck. She decided to change from Margot to a Gallic spelling in honor of the red Bordeaux her parents said they drank on the night of her conception. Suddenly she is on the cover of Women's Wear Daily, jetting off to Key West for 12 pages in Town & Country, then over to Mexico to water ski for SPORTS ILLUSTRATED. Both Vogue and Harper's Bazaar have Margaux covers ready for possible use early next year; ad agencies are queuing up to get Margaux to model everything from liquor to sportswear. She has had her first film test. Out of this whirl will come at least $200,000 in commissions next year—and the kind of glory that maybe shouldn't be squandered on 19-year-olds.

In the heady world of fashion it can sometimes happen like that. "When I first saw her at Halston's party for Liza Minnelli," coos top fashion photographer Francesco Scavullo, "I flipped. I'm always looking for faces. You don't see one like hers in 10 years." Chimes in Carrie Donovan, fashion editor of Bazaar, "If she can communicate that VROOM in photographs, she has one helluva career ahead."

Just how does the fashion consistory decide to elect a new superstar? She is often not a professional model, as witness such recent symbols of beauty as Baby Jane Holzer, Marisa Berenson or Countess Christina Paolozzi. The Girl of the Hour must have some special quality—and, in Margaux's case, it is an abundance of healthy outdoor good looks plus breezy affability fresh off the ski slopes—with the vocabulary of "real neat" and "fabulous" that goes with it. Plus the prestige of being Hemingway's granddaughter.

"My name?" Margaux says. "Of course it helps. If you've got it, use it. I'm proud of it, for sure. Not because of Granddad, but because of Dad. He's got good style points. He lives exactly the way he wants to."

Still and all, Margaux Hemingway, just two years out of Catlin Gabel private school in Portland, Oreg., might easily be nothing more this winter than somebody's college date. But a man appeared out of the blue—and has made all the difference. He is Errol Wetson, 33-year-old founder of an East Coast hamburger chain and former owner of a beautiful people Manhattan watering hole, Le Drugstore.

Wetson first spotted Margaux last May in the Palm Court of the Plaza Hotel. "She looked like pure Americana to me," he recalls. Borrowing a scene from a '30s musical, he turned up outside her hotel room with a single rose, a bottle of champagne and a silly grin. Of course, it worked. Romance bloomed (the two are now roommates in Prince Egon von Furstenberg's old apartment). When Wetson asked Margaux what she wanted—a model's career, TV, the movies?—she offered a reply that would have pleased granddad: "All of it!"

Margaux took a teenage summer off—working in California as a chauffeur for actor George C. Scott's daughter—but upon her return to New York in November, the sky ride began under Wetson's cool supervision. First, she signed on at a top modeling agency, Wilhelmina, where she was ordered to pluck her eyebrows (she refused) and diet down to a "fighting weight" of 136 pounds (Margaux is almost there). No one worried about her height.

Most important was the agency's enthusiasm. "She's part of the nostalgia thing," exclaims the agency's codirector Bill Weinberg. "She's a latter-day blue blood whose ancestry is literary royalty. Sure she sounds a little like a hillbilly, but she's authentic—a country kid young people can relate to."

As Margaux would say (and, regrettably, often does), "That's for sure." In Ketchum, Idaho, her dad taught her to shoot, ride, catch trout, ski and "drink tequila at a cowboy bar." Ernest Hemingway is a dimmer figure (he died when Margaux was 6). She remembers him in Cuba as "big and burly—I used to sit on his knee. I never connected him with suicide until four years ago."

Right now the man in her life is Wetson. "We're in love," she glows. Marriage? Certainly not until after he has met mom and dad in Ketchum. And kids? "Well, some time, but right now I'm just a kid myself." Some kid! As an old pal of Ernest Hemingway's replied when asked what Papa would think of his granddaughter now, "I suspect he'd like everyone to think he sired her."