J.K. Rowling during the launch of online Web site Pottermore in London last June. (Susanne Plunkett/REUTERS)

There’s an entire ecosystem of Twitter users who tweet as their favorite characters from the “Harry Potter” books, sometimes for humor and sometimes for interactive fan fiction dialogues with the other impersonating accounts.

Upon hearing that the new book wouldn’t have anything to do with Harry Potter, here’s how the cast of characters reacted: