The cast of “Harry Potter and the Cursed Child” includes Jamie Parker (Harry), Sam Clemmett (Albus) and Poppy Miller (Ginny). Previews for the play began Tuesday. (Charlie Gray)

The curtain has risen on Harry Potter’s latest adventure — and author J.K. Rowling is urging fans not to ruin the magic by letting its secrets out.

“Harry Potter and the Cursed Child” has had its first preview at Palace Theatre in London, England, with audience members given buttons urging them to #keepthesecret.

In a recorded message, Rowling encouraged theatergoers to “let audiences enjoy ‘Cursed Child’ with all the surprises that we’ve built into the story.”

The drama — staged as two plays — picks up the story 19 years after Rowling’s last Potter novel. Its characters include the adult Harry and his younger son, Albus Severus Potter, a student at Hogwarts school.

A synopsis says Harry is now an overworked civil servant in the Ministry of Magic, while his son is struggling “with the weight of a family legacy he never wanted.”

The play, staged at the Palace Theatre in London, England, will officially open July 30. (Jack Taylor/Getty Images)

The Daily Telegraph said Wednesday that audience members were “in raptures” after Tuesday’s performance, the first night of almost eight weeks of previews.

Rowling has long insisted there will be no new Harry Potter novels, so excitement about the new stage story is stratospherically high.

Rowling worked on the story for the drama, which has a script by Jack Thorne, a stage and screen writer.

The cast includes British actor Jamie Parker as Harry. Swaziland-born actress Noma Dumezweni plays Harry’s brainy friend Hermione, a role played in the movies by Emma Watson.

Rowling has said she is disappointed by those who have criticized the casting of a black actress. She said Hermione’s race was never specified in the books and told the Observer newspaper that “Hermione can be a black woman with my absolute blessing and enthusiasm.”

The plays officially open July 30, and the script will be published the next day.