“Harry Potter” author J.K. Rowling excited fans Thursday when she revealed she was writing a book. The British author tweeted the message on World Book Day.

After the best-selling author, 49, made the announcement, she began to retweet posts by fans who showed pictures of themselves dressed as “Harry Potter” characters in honor of World Book Day. Subsequently, she retweeted a photograph of “Harry Potter” actor Chris Rankin, who played Percy Weasley in the blockbuster films, with a girl who appeared to be dressed as Narcissa Malfoy.

Rowling then took a moment to joke about the odd pairing:

Although the last “Harry Potter” novel was released in 2007, Rowling’s followers still seem thrilled by the idea she may returning to the series. The tweet spawned tons of replies asking her to stop teasing and start writing more books for the boy wizard series.

So if Rowling was only kidding about a prequel, then what was she writing on World Book Day? Fans who closely follow Rowling on Twitter know she is working on her next book in the “Cormoran Strike” series. She started to publish the novels in 2013 under the pseudonym Robert Galbraith. The novel will be the third in the series, and Rowling has been working on it for several months now.

Looks like interested readers will just have to find their Percy/Narcissa stories in fan fiction.