After reading briefly from the final book, "Harry Potter and the Deathly Hallows," she took questions from audience members.

She was asked by one young fan whether Dumbledore finds "true love."

"Dumbledore is gay," the author responded to gasps and applause.

She then explained that Dumbledore was smitten with rival Gellert Grindelwald, whom he defeated long ago in a battle between good and bad wizards. "Falling in love can blind us to an extent," Rowling said of Dumbledore's feelings, adding that Dumbledore was "horribly, terribly let down."

Dumbledore's love, she observed, was his "great tragedy."

"Oh, my god," Rowling concluded with a laugh, "the fan fiction."

Potter readers on fan sites and elsewhere on the Internet have speculated on the sexuality of Dumbledore, noting that he has no close relationship with women and a mysterious, troubled past. And explicit scenes with Dumbledore already have appeared in fan fiction.

Rowling told the audience that while working on the planned sixth Potter film, "Harry Potter and the Half-Blood Prince," she spotted a reference in the script to a girl who once was of interest to Dumbledore. A note was duly passed to director David Yates, revealing the truth about her character.

Rowling, finishing a brief "Open Book Tour" of the United States, her first tour here since 2000, also said that she regarded her Potter books as a "prolonged argument for tolerance" and urged her fans to "question authority."

Not everyone likes her work, Rowling said, likely referring to Christian groups that have alleged the books promote witchcraft. Her news about Dumbledore, she said, will give them one more reason.