"We set a trilogy as a placeholder because we knew there would be more than one movie, but we're pretty sure it's going to be five movies," said JK Rowling
Arriving for the opening gala, creator JK Rowling told the Press Association that she was "so happy" that fans had heeded her pleas to keep the plot a secret, and said she hoped the play would one day appear on Broadway
"Scotland will seek independence now. Cameron's legacy will be breaking up two unions. Neither needed to happen," J K Rowling wrote on Twitter
"You've been amazing for years at keeping Harry Potter secrets so you didn't spoil the books for readers who came after you," Ms Rowling said in the video message