JK Rowling has announced a new instalment of her best-selling Harry Potter series.

The famous author took to Twitter yesterday to announce she is working on a Harry Potter play.

The play is called “ Harry Potter and the Cursed Child ” and will open in London’s West End next year.

In a series of tweets Rowling teased fans with vague details about the project.

“I don't want to say too much more, because I don't want to spoil what I know will be a real treat for fans,” she wrote.

“I can say that it’s not a prequel!”

Rowling will be collaborating with theatre veterans Jack Thorne and John Tiffany on the project.

Tiffany, a Tony award winner, will direct the play and Tiffany will be working with Rowling on the script.

The play will be produced by Sonia Friedman, who has 120 plays to her name.

Popular singer/songwriter Imogen Heap is also involved in the project as the head of music.

While details of the storyline are sparse Rowling did confirm she believes a play is the best medium for the story she wants to tell.

“To answer one inevitable (and reasonable!) question - why isn't #CursedChild a new novel?

“I am confident that when audiences see the play they will agree that it was the only proper medium for the story.”

Thousands of fans responded to the announcement on Twitter, with many international Harry Potter lovers making plans to travel to England for the show.

Others were worried they would not make it to London for the show.

Rowling admitted to having received countless offers to continue Harry’s story over the years but believes Thorne, Tiffany and Friedman are a dream team.