In a brief online video message posted Monday, Rowling said: “You’ve been amazing for years at keeping Harry Potter secrets so you didn’t spoil the books for readers who came after you, so I’m asking you one more time to keep the secrets and let audiences enjoy 'Cursed Child' with all the surprises that we’ve got to the story. Thank you.”
The story is set 19 years after "Harry Potter and the Deathly Hallows" and features Harry as a Ministry of Magic employee. Poppy Miller also stars as Ginny and Sam Clemmett as Albus Severus.
Scripts will be available to buy worldwide from July 30.
Plot-spoilers and cellphone recordings of performances have long been an issue in London's West End and Broadway, even after nightly warnings to theatergoers to switch off their devices.