Once upon a time, Carrie Bradshaw was a virgin.

Hard to believe. When viewers met her 15 years ago in HBO's hit comedy "Sex and the City," Carrie, as played by Sarah Jessica Parker, was a self-styled "sexual anthropologist" who wrote a newspaper column based on her ongoing "research," ably assisted by her friendship with three gal pals.

Now comes a new series that does for Carrie Bradshaw what "Superboy" comics did for Superman. "The Carrie Diaries" turns back the clock to the high school blossoming of Carrie as a writer, woman and passionate would-be Manhattanite.

"The Carrie Diaries" could easily have been a needless prequel to the original's six seasons, an extension of a brand that, by some appraisals, had already overstayed its welcome as two feature films in 2008 and 2010.

Instead, this new hour-long drama, which premieres Monday at 8 p.m. on the CW, is pretty terrific and remarkably faithful to its heroine. If "Sex and the City" has a soul, then "The Carrie Diaries" has tapped it.

The series can boast key pieces of the original's DNA, including executive producers Amy Harris and Candace Bushnell, the real-life columnist who created Carrie Bradshaw.

Another winning ingredient: its star, AnnaSophia Robb, who serves as a perfect proto-Sarah Jessica Parker. Watching "The Carrie Diaries" in its circa-1984 Connecticut environs, you believe that this is the girl who would become the Carrie you know so well.

"This is a Carrie who isn't sure of her creative voice, her sexuality, her way of dressing," Robb points out. "I think it will be fun for the original 'Sex and the City' audience to see what Carrie was like in her younger days - what made her fall in love with New York and why her relationships are so riddled with problems.

"And it introduces the franchise to a whole new audience that's never seen 'Sex and the City.'"

That, of course, represents a big chunk of the CW demo. It includes Robb, now 19, who, not so long ago, had never seen the often racy, progenitor of the show she soon would be starring in.

"My mom wouldn't let me. I was too young," she explains. "But once I heard they were making 'The Carrie Diaries,' I bought all the seasons of 'Sex and the City' on iTunes and realized, 'Omigod, this is such a brilliant show!'"

It's around 5 p.m. as Robb, having finished an unusually "short" recent workday, is nursing a fruit smoothie at a diner she frequents near her downtown Manhattan digs.

She is wearing a Breck (Breckenridge) T-shirt that reflects her Colorado roots, black leggings and vibrant cobalt-blue fingernail polish (the latter required for Carrie). She has an impossibly angelic face and enormous green eyes and, though petite at 5-feet-2, seems poised to be the next big thing.

One clue: That very morning, a paparazzo had greeted her outside her apartment for the first time.

"I find it a bit peculiar," she concedes. "Until now, I don't think any of them really cared."

This is not to suggest that AnnaSophia Robb is a show-biz newcomer. At 9, the little girl who was determined to act was journeying with her parents from her Denver home to Los Angeles, where, right away, she booked a McDonald's commercial.

Soon after, she landed a starring role in "Because of Winn-Dixie." Her dozen films also include "Charlie and the Chocolate Factory," "Sleepwalking" and "Soul Surfer," in which she played the real-life surfer who lost an arm to a shark but didn't lose her love of surfing.

A year ago, Robb was waiting for responses to her college applications when she got a peek at the "Carrie Diaries" script.

"I decided that college is always going to be there, while this show was a once-in-a-lifetime opportunity." She laughs. "I also knew my getting the role was a super-long shot."

But after a week of auditioning, she got the part. The pilot was shot last March, and the series got picked up by the network in May. Production resumed in October.

"The Carrie Diaries" begins on the first day of Carrie's junior year in high school. It's a painful time: Carrie and her 14-year-old little sister (Stefania Owen) lost their mother to cancer three months earlier, so the household now includes only these sisters and their father (Matt Letscher).

As in "Sex and the City," this series features Carrie's epigrammatic narration. She describes the scene at school with "everyone passing around news of the day like mono after a homecoming dance," then adds, "I realized that I was the virus no one wanted to get near: the freak who had lost her mom."

Carrie meets a new student (Austin Butler), whom she fancies. But an even bigger crush is Manhattan, where she lands an internship and meets an exciting mentor: the cool style editor at Interview magazine (Freema Agyeman). Carrie declares that the "man" she'll be losing her virginity to is Manhattan.

Fifteen years ago in a SoHo restaurant five minutes away, Sarah Jessica Parker was having lunch with this same reporter as she worried how viewers would receive "Sex and the City," her new show.

"We want the audience to see this as provocative and sophisticated, not gratuitous and vulgar," she said.

Mission accomplished. Now "The Carrie Diaries" arrives as a prelude, with sweetness and a sense of wonder radiated by its luminous young star.

"I felt like this was a character that I would be able to play for a long time," says Robb, the new Carrie Bradshaw. "I will be able to grow with her."