Both director John Tiffany and playwright Jack Thorne are being credited as co-writers too, granting them unprecedented ability to help shape the tale. Tiffany has developed a reputation for "major-event" theatre, from his breakthrough Black Watch to the folky, feelgood musical Once.

He has said: “I’m conscious of bringing the fans what they love, doing this story justice and exploring the psychology of a grown up Harry Potter with the same epic sweep as the books and the films, but in a different way.”

He added: "I knew from seeing the excitement in the kids I’d shared the books with that we had to bring darkness back. There had to be new jeopardy.”

Thorne, 37, enjoyed a West End transfer with his 2013 adaptation of Swedish vampire flick Let the Right One In, directed by Tiffany (but he has made a bigger name for himself in TV working with Shane Meadows on the This Is England series). A fan to his bones, he declared: "I’d read all the books in my 20s and I’d go to the cinema and watch all the films by myself. I was deeply in love with Potter already, so the chance to do this..."

So, not Sir Trevor Nunn directing, or Simon Stephens writing…?

No, lesser-known names. And that applies to the casting too: Jamie Parker, cast as Harry, Noma Dumezweni (Hermione) and Paul Thornley (Ron) are not the sort of leads who in themselves will get the cash-tills ringing. But they are now poised to leap several notches up the fame ladder if all goes well.

Tiffany and team have struck a blow for diversity by casting the Swaziland-born Dumezweni as Hermione. While some took to social media to complain at this divergence from the Emma Watson ‘template’ on film, the more clued-up and fair-minded fans enthused about the decision.

Furthermore, faster than one could shout Expelliarmus!, Rowling tweeted: “Canon: brown eyes, frizzy hair and very clever. White skin was never specified. Rowling loves black Hermione.”

If Helen Mirren can play the Queen, then Dumezweni can play Hermione. It’s theatre, dear.