JK Rowling has announced her Harry Potter stage play will open in London's West End next year.
Called Harry Potter and the Cursed Child, it will tell the "untold part" of the boy wizard's story, including the story of the lives of his murdered parents.
However, the author said on Twitter the play was "not a prequel".
It will run at the Palace Theatre in the summer of 2016, with tickets on sale this autumn.
Rowling said she chose to make the announcement on Friday because it was "a very special day" - the 18th anniversary of when her debut book, Harry Potter and the Philosopher's Stone, was first published in the UK.
But she was tight-lipped about the plot of the play, saying she did not "want to say too much more, because I don't want to spoil what I know will be a real treat for fans".
She added: "To answer one inevitable (and reasonable!) question - why isn't Cursed Child a new novel? I am confident that when audiences see the play they will agree that it was the only proper medium for the story."
The play was first announced in December 2013, after the author said she had "received countless approaches" over the years "about turning Harry Potter into a theatrical production".
Although the new story has not been written by Rowling, it is a collaboration between herself and writer Jack Thorne - who previously adapted Let The Right One In for the stage and won a Bafta for his work on Channel 4's This is England '88 - and John Tiffany, who will also direct the play.
It will be produced by Sonia Friedman and Colin Callender, and British singer Imogen Heap will provide the music.
Analysis - Tim Masters, entertainment correspondent
The plot details might still be hazy, but there's little doubt Harry Potter and the Cursed Child will have a magical effect at the West End box office.
It will be at the 1,400-seat Palace Theatre, which was home to theatrical blockbuster Les Miserables for a record 19 years.
JK Rowling's success needs no introduction, but the new Harry Potter play reunites the creative dream team behind the stage adaptation of supernatural love story Let The Right One In.
When it comes to West End hits, producer Sonia Friedman has a golden touch. Her biggest successes include Book of Mormon and Sunny Afternoon, while her musical Bend It Like Beckham kicked off to rave reviews this week.
When it opens in summer 2016 the play is likely to spark the kind of Potter-mania that surrounded the release of the books and films.
And it won't end there. The stage show will be closely followed by the Potter film spin-off Fantastic Beasts and Where to Find Them in November 2016.
"Jack, John and Sonia Friedman are a dream team," Rowling said.
"It has been a huge pleasure to share with them (and soon, with you!) this untold part of Harry's story."
Producers originally said the play would explore "the previously untold story of Harry's early years as an orphan and outcast".
"Featuring some of our favourite characters from the Harry Potter books, this new work will offer a unique insight into the heart and mind of the now legendary young wizard," they said.
The Daily Mail's Baz Bamigboye claimed The Cursed Child would "delve into what happened to Harry's parents before they were killed by Lord Voldemort, forcing an infant Harry to be raised in miserable circumstances by his mother's sister, Petunia, her horrid husband Vernon and their spoiled son Dudley".
Rowling's seven Harry Potter best-sellers were adapted into eight blockbuster films starring Daniel Radcliffe as the boy wizard.
The author is making her screenwriting debut on Potter spin-off film Fantastic Beasts and Where to Find Them, starring Eddie Redmayne, due in cinemas next November.