'Harry Potter and the Cursed Child' is a sequel that takes place 19 years (!) after the final book. The play starts with the closing bit of the final book where adult Ron, Hermione, Harry and Ginny send their children off to Hogswarts.
The play starts 19 years after the final book, but then quickly jumps another 4 years when Albus (Harry and Ginny's son) is in his final year at Hogwarts
She oversaw the script but J.K. didn't actually write it
'Harry Potter and the Cursed Child' is a play currently on in London in two parts. They haven't got plans to turn it into a film (yet) but if you can't make it to the show, you can buy the script as a book to read. It's already sold 2 million copies!
Grown up Hermione, Ron and Harry are played by Noma Dumezweni, Paul Thornley and Jamie Parker. Here they are all together.