JK Rowling appears to have recorded a significant victory in her ongoing Twitter spat with Piers Morgan.
The pair have been trading insults for months, with Morgan saying he had never read a line of Harry Potter.
It intensified when they took shots at each other over Donald Trump's travel ban.
Then on Valentine's Day, Rowling tweeted a screenshot of an article praising her which she said was anonymously sent by an admirer.
The author said she would love to know who wrote it so she could thank them.
An irritated Morgan responded by tweeting: "Priceless #humblebrag BS. Nobody plays the celebrity game more abusively or ruthlessly than you, Ms 'Intensely Private Billionaire'."
However, it turns out the article, about 100 top British celebrities, was written by Morgan himself back in 2010.
In it Morgan wrote: "She's sold over 400 million copies of her Harry Potter books, and also the movie rights for some of the biggest-grossing films in history, creating a global brand that's worth an estimated £7bn, making her over £500m personally.
"She's won squillions of awards; and she was even named the 48th most powerful celebrity in the world by Forbes magazine. So Ms Rowling definitely matters."
Twitter users could not wait to point out the apparent error.
"Oh my god. Oh my god. Oh my god. He doesn't realise. This is the best day of my life," wrote one.
Another said: "You'll find she's just run him over, had him stuffed; he's now above her mantle #killerblow."
Morgan has since claimed he was aware it was his article and that he had not been fooled.
"Love how many people genuinely think I was 'tricked' by JK Rowling yesterday," he tweeted.
"They've been reading too much Harry Potter - dumbs the brain."
The spat between the celebrity pair has prompted a bookshop owner to tweet every line of the first Harry Potter book to Morgan.