A computer hacker has posted on a website what he says is the ending of the final Harry Potter novel.
Rowling finished writing the final book in January
He claims to have hacked into the computer system at publishers Bloomsbury and knows who dies in Harry Potter and the Deathly Hallows.
A spokeswoman for Bloomsbury played down the claims, saying there were "lots of rumours on the internet."
Author JK Rowling has already said that two characters will die in the book, which is published on 21 July.
A spokesman for the book's US distributor, Scholastic, said: "There is a whole lot of junk flying around. Consider this one more theory."
The hacker - who calls himself "Gabriel" - said he posted the spoiler "to make reading of the upcoming book useless and boring."
Rowling told fans last month to be wary of false rumours regarding the plot.
"There will always be sad individuals who get their kicks from ruining other people's fun," she said on her website.
She hoped, however, that her readers would "embark on the last adventure they will share with [Harry] without knowing where they are they going."
JK Rowling has said she will miss Harry Potter
Rowling is to take part in a marathon overnight autograph session in London to celebrate the publication of the final book.
The author will read from Harry Potter and the Deathly Hallows at the Natural History Museum at midnight on 21 July.
She will then meet 1,700 fans and sign their copies of the book in a session that is expected to last until dawn.
The fans will be chosen in a ballot.
The Potter books have sold 325 million copies worldwide, have been translated into 64 languages and spawned five films.
The fifth film, Harry Potter and the Order of the Phoenix, will be in cinemas next month.