Nearly eight weeks of previews and months more of fans’ excitement will finally culminate in the official debut of J.K. Rowling’s now grown-up boy wizard at the opening gala of Harry Potter and the Cursed Child today.

Taking place on the eve of the joint birthday of Harry and his creator Rowling, the doors to London’s Palace Theatre will – like Platform 9 3/4 of Kings Cross Station before them – provide the gateway for fans to return to the magical world of Harry, Ron, Hermione and their beloved Hogwarts on Saturday.

The two-part play, which stretches over five hours, is set 19 years after the events of the seventh and final book, with Ministry of Magic employee Harry and his wife Ginny waving off their youngest son Albus Severus to school.

But at Hogwarts, Albus struggles with the weight of his family legacy and goes to extreme and dangerous lengths to right the wrongs of the past.

Co-devised by Rowling, written by Jack Thorne and directed by John Tiffany, it appears an Obliviate charm worthy of Gilderoy Lockhart would be required for critics to forget the “spell-binding” and “out of this world” experience.

Daily Telegraph critic Dominic Cavendish said that “British theatre hasn’t known anything like it for decades”. He raved: “It’s a triumph. Not an unqualified one – there are some quibbles – but in all key respects, it grips, it stirs, it delights.”

It’s quite apparent this isn’t written to be either a book or a tie-in film; it’s a spectacle for the theatre

The Independent’s Jack Shepherd similarly awarded the play five stars, writing: “It’s quite apparent this isn’t written to be either a book or a tie-in film; it’s a spectacle for the theatre, one that is filled to the brim with fan service and magical imagery.”

Special praise has gone to Sam Clemmett, who plays Albus, and Anthony Boyle as Draco Malfoy’s son Scorpius, while Jamie Parker, Paul Thornley and Noma Dumezweni play the adult stars of the saga: Harry, Ron and Hermione.

Jamie Parker in the role of adult Harry Potter.

As the clock turns midnight tonight, those who wish to keep forever the eighth story in the cannon can purchase the script of the two-part play.

Bookshops are hosting midnight book release parties, as they did for each new novel during the height of Pottermania.

Those eager to find out what happens in the time-twisting instalment can read the review of 10-year-old Toby L’Estrange, a speed-reading prodigy who has been challenged by Amazon to write the first review of the new Harry Potter story.

Despite the script’s release, stage play audiences will still be urged to “keep the secret” as they leave.

Keeping the play spoiler-free is all the more important as producers announce another 250,000 tickets are set to go on sale next week, keeping it running until December 2017.

More tickets will be made available from 11am next Thursday.