In a interview with CNN, [J.K. Rowling] revealed that she has wroten a manuscript that may not be ever published. A huge part of that story was writen in dress as a part of a costume for her birthday party.
When Christiane Amanpour asked about a possible political book for children that she was considering writing, Rownling told:”Oh, that was a fairy tale … But I — I will tell you this. On my 50th — the theme of my 50th birthday, which I held at Halloween, even though that’s not really my birthday, was come as your own private nightmare. And I went as a lost manuscript. And I wrote over a dress most of that book. So that book, I don’t know whether it will ever be published, but it’s actually hanging in a wardrobe currently.”
During the interview, she talked mainly about Lumos, the charity institution which she is founder and president and tries to do away with children and teenagers’ institutionalization.
While the dress still inside the wardrobe like a Boggart, we can only try to imagine what the story was about.