(CNN) It was a big weekend for Harry Potter fans.
Nearly ten years since the final book J.K. Rowling wrote for the franchise, a new installment, "Harry Potter and the Cursed Child," dropped at midnight. The timing was fitting -- Sunday is Potter's birthday, and Rowling's.
Fans of the series flocked to bookstores around the world wearing wizard hats and capes to get their hands on a copy.
"It's time to go back to Hogwarts," tweeted one excited Potter reader.
Another tweet read, "If anyone tries to reach me and I don't answer in the next few weeks, don't worry! I'm back at Hogwarts."
Many social media comments echoed the sentiment in a tweet that read, "I've been waiting for this for 10 years."
The book is not a novel, and it's not written by Rowling. Instead, it's the script of a stage production of the same name, currently running in London. Rowling's hand isn't totally absent from it, though -- playwrights Jack Thorne and John Tiffany collaborated with her for the story.
Rowling attended the play's premiere on Saturday and revealed that the show marks the end of Potter's adventures.
"He goes on a very big journey during these two plays and then, yeah, I think we're done," Rowling told Reuters. "This is the next generation, you know. So, I'm thrilled to see it realized so beautifully but, no, Harry is done now."
The plot picks up where the epilogue of "Harry Potter and the Deathly Hallows" left off, 19 years after Voldemort's defeat. Potter now has three children and works at the Ministry of Magic.
Based on preorder sales, "Harry Potter and the Cursed Child" could become the top selling book of 2016 for both Amazon and Barnes & Noble.
The book comes at a time of renewed interest in Potter and his adventures.
This fall, Warner Bros. (which, like CNN, is owned by Time Warner) is releasing "Fantastic Beasts and Where to Find Them," a film based on Rowling's hit 2001 book, about the magical creatures in the world of Harry Potter. It'll star Eddie Redmayne and Colin Farrell.