J.K. Rowling broke down in tears when she visited the tiny apartment she wrote the original "Harry Potter" book in.

The author was a single mother living on benefits in the cramped home, near Edinburgh, Scotland, when she began writing the first novel about the schoolboy wizard - "Harry Potter and the Philosopher's Stone".

The book series has gone on to sell over 400 million copies worldwide, earning her an estimated $1 billion fortune.

Rowling now lives in a nearby mansion and had not been back to the property since moving out at a decade ago, until she revisited it with a camera crew for the British TV show "A Year in the Life of J.K. Rowling".

Upon her return, she said, "I feel I really became myself here. This is where I turned my life around. I'd made such a mess of things. So I just thought, 'Well, I want to write - and I wrote the book.' "

Rowling first moved into the flat with daughter Jessica after splitting from Portuguese husband Jorge Arantes.

When visiting one room, she said, "Now this is really freaky. This is the room where I finished 'Philosopher's Stone'. I didn't know then there would be a fairytale ending!"

Rowling now lives in 19th Century estate house, Killiechassie House, with second husband Neil Murray, and the couple's two children, David and Mackenzie, and her daughter Jessica.