"I am sorry to tell you all that Sue passed away last night after a two-year battle with cancer," Clark wrote on Grafton's official Facebook page.
"She was surrounded by family, including her devoted and adoring husband Steve. Although we knew this was coming, it was unexpected and fast."
Grafton died at Cottage Hospital in Santa Barbara, California, after battling cancer of the appendix, Alexis Welby, director of publicity at her publisher, G.P. Putnam's Sons, told CNN.
Grafton started the alphabet novels
in 1982, according to the author's webpage
. All of them featured private eye Kinsey Millhone, a former police officer who was a quiet rebel. Millhone has trouble dealing with bureaucracy and "an aversion to cooking, a lack of interest in fashion, and an affinity for books," Grafton wrote in a brief biography of Millhone.
Grafton's last alphabet mystery was published last August. "Z Is for Zero" was tentatively scheduled to come out in 2019.
"Many of you are asking (some quite plaintively) what I intend to do when I get to 'the end' of the alphabet," Grafton wrote on her webpage. "I've been consistent in my response which is 'no clue.' I want to see what kind of shape I'm in mentally and physically."
Other mystery writers posted online tributes. Lisa Scottoline tweeted: "Very sad to hear that the wonderful Sue Grafton has passed. She forged a path for women in crime fiction, and all of us followed and adored her. Deepest condolences to her family."
Sara Paretsky, whose protagonist is named V.I. Warshawski, tweeted: "I'm deeply grieved to learn of Sue Grafton's death. Kinsey and VI were both born in 1982 and our writing worlds have been closely twined ever since. This is a grievous loss."
Grafton was born on April 24, 1940, in Louisville, Kentucky, and graduated from the University of Louisville. Her father was an attorney and mystery writer, the Internet Movie Database said.
Grafton wrote several other novels as well as screenplays for television, such as "Lolly-Madonna XXX" in 1973 and "Love on the Run." She explained why she was devoted to mysteries: "The mystery novel offers a world in which justice is served. Maybe not in a court of law, but people do get their just desserts."
She was married to Steve Humphrey for more than 35 years and had three children, four granddaughters and one great grandson, the website said.
The Facebook message from her daughter said:
"She had been fine up until just a few days ago, and then things moved quickly. Sue always said that she would continue writing as long as she had the juice. Many of you also know that she was adamant that her books would never be turned into movies or TV shows, and in that same vein, she would never allow a ghost writer to write in her name.
"Because of all of those things, and out of the deep abiding love and respect for our dear sweet Sue, as far as we in the family are concerned, the alphabet now ends at Y."