Francine Pascal, mastermind of the long-running, best-selling, and much-beloved Sweet Valley High series of young-adult books, died Sunday in Manhattan at the age of 92, according to The New York Times.

Per the report, Pascal’s daughter, Laurie Wenk-Pascal, confirmed to the outlet that her mother died of lymphoma at NewYork-Presbyterian Hospital.

Born Francine Paula Rubin on May 13, 1932, in Manhattan, Pascal first studied journalism at New York University before writing as a freelancer for the likes of gossip outlets True Confessions and Modern Screen, and eventually magazines such as Cosmopolitan and Ladies’ Home Journal.

In the 1960s, she and her second husband, journalist John Pascal (who died in 1981), wrote for the soap opera The Young Marrieds. “It was something neither of us cared about,” she told Entertainment Weekly in a tell-all interview in 2019. “We needed the money.”

Around the same time, the couple wrote the book for the Broadway musical George M!, about the life of musical-theater icon George M. Cohan, with her brother, Tony-winning librettist Michael Stewart. After the musical, Pascal said she got the idea for a book about a teenage girl who couldn’t stop fighting with her mother, which led to her writing three books in the Victoria Martin series. The first entry, Hangin’ Out With Cici, was adapted into the 1981 ABC Afterschool Special My Mother Was Never a Kid.

After the success of Cici and her 1980 novel The Hand-Me-Down Kid, Pascal pitched the idea for a soap opera TV series that centered on high school teenagers but the networks “were not interested,” according to Pascal who said they thought “it was too girly.”

But, this rejection would ultimately lead to the series for which she would become best known, Sweet Valley High, which centers on the lives of identical twins Jessica and Elizabeth Wakefield, who live in the fictional Los Angeles suburb of Sweet Valley.

As she explained it to EW: “A friend of mine had lunch with a [book] editor, a man, who said, ‘Why isn’t there a Dallas for young people?’ I thought about it, and I actually had a book [proposal] due. There are a lot of twins in my life. [My agent] Amy [Berkower] is a twin. My sister-in-law was a twin. People are always fascinated by twins. You’ll never be alone. [Laughs] I thought about it, and this other soap opera thing was in my head, the one that I couldn’t sell. I sat down and I wrote a [character] bible and the first 12 [SVH] stories. It went quickly because it was such a fertile idea. Bantam Books loved it. They ordered all 12.”

The series, which first had its debut in 1983, spawned multiple spin-offs, ran for 20 years, was translated into 27 languages, and reportedly sold 150 million copies worldwide. Sequels The Sweet Valley Confidential and The Sweet Life were published in 2011 and 2012 and followed the girls as adults. A Sweet Valley High TV series ran from 1994 to 1997 in syndication and briefly on UPN.

Speaking with EW about the longevity of the SVH franchise, Pascal said, “The saying ‘The more things change, the more things stay the same’ really applies to those years. There’s such similarity, no matter how different today’s teenager thinks she is. She’s the same in here [points to her heart] and in here [points to her head] as I was — but the clothes are different.”

Non-SVH projects of Pascal’s included the Fearless books series, adult novel If Wishes Were Horses, psychological thriller Save Johanna!, and YA book The Ruling Class.

Pascal is survived by daughters Laurie and Susan, as well as six grandchildren and five great-grandchildren.