The 50-year-old British novelist made the revelation while correcting a fan, who thought that her new play, "Harry Potter and the Cursed Child," will also be a film.
"You heard wrong, I'm afraid. "#CursedChild is a play. #FantasticBeasts will be 3," she wrote.
Starring Eddie Redmayne as Newt Scamander, "Fantastic Beasts and Where to Find Them," is the first installment. It is scheduled to release on November 18.
Rowling's new play, "Harry Potter and the Cursed Child," is the official eighth Potter story and is set to open in London on July 30. It picks up the boy wizard's story 19 years after the end of "Harry Potter and the Deathly Hallows".