Harry Potter fans asked to keep secrets ahead of Cursed Child premiere

The next chapter in the Harry Potter story is set to be revealed on stage after months of anticipation, the BBC reports.

The first preview for Harry Potter and the Cursed Child will take place in front of an audience of 1,500 at London's Palace Theatre on Tuesday night.

The play, by Jack Thorne, is set 19 years after the seventh and final book in the series by JK Rowling.

Rowling has asked audiences not to reveal details of the story.

"You've been amazing for years at keeping Harry Potter secrets so you didn't spoil the books for readers who came after you," she said in a video message.

"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 built into the story."

The play is the eighth story in the series and the first time an official Harry Potter story has been presented on stage.

Thorne's two-parter, written in collaboration with Rowling and director John Tiffany, will feature a cast of more than 30 actors.

Picking up from where the Deathly Hallows epilogue left off, it portrays Harry, played by Jamie Parker, as an "over-worked" employee at the Ministry of Magic.

The story will explore how his youngest son Albus (Sam Clemmett) deals with the "heavy burden" of the Potter family legacy.

Other familiar characters include Hermione Granger (Noma Dumezweni), Ron Weasley (Paul Thornley), Ginny Potter (Poppy Miller) and Draco Malfoy (Alex Price).

Rowling on Tuesday tweeted a good luck message to Anthony Boyle, who plays Draco's son Scorpius.

In an interview with The Observer, Rowling spoke of her frustration at online reaction by "a bunch of racists" to the casting of a black actress in the role of Hermione.

Olivier winner Dumezweni "was the best actress for the job," she said.

The best-selling author added: "I think that, as a theatrical experience, as a play, it will be unlike anything people have seen before."

When tickets went on sale last October the first 175,000 sold within 24 hours. The script is already topping bestseller lists, although it won't be published until after the play's official opening on 30 July.

Those who did manage to get tickets have been asked to arrive at the theatre an hour before the performance due to security checks.

The Harry Potter books have sold more than 450 million copies since 1997 and been adapted into eight films.