She made her revelation to a packed house in New York's Carnegie Hall on Friday, as part of her US book tour. She took audience questions and was asked if Dumbledore found "true love".

"Dumbledore is gay, " she said, adding he was smitten with rival Gellert Grindelwald, whom he beat in a battle between good and evil wizards long ago. "Falling in love can blind us to an extent, " she said, and added Dumbledore was "horribly, terribly let down" and his love for Grindelwald was his "great tragedy".

"Oh, my god, " Rowling, 42, concluded with a laugh, "the fan fiction".

Fan sites have long speculated on Dumbledore's sexuality as he was known for having a mysterious, troubled past.

Rowling told the audience that while working on the planned sixth Potter film, Harry Potter and the Half-Blood Prince, she saw that the script carried a reference to a girl who was once of interest to Dumbledore.

She said she ensured director David Yates was made aware of the truth about her character.

Rowling also did a brief reading from the seventh book in her best-selling series, Harry Potter and the Deathly Hallows, as part of her Open Book Tour of the US . . . her first there for seven years. She said she regarded her novels as a "prolonged argument for tolerance" and urged her fans to "question authority". But she added that not everyone likes her work. Christian groups have alleged the books promote witchcraft. The author said her revelation about Dumbledore would give them one more reason.