Author J.K. Rowling was so upset about killing off one of the main characters in her latest Harry Potter saga that she burst into tears.

But the creator of the teenage wizard said it was vital to be strong because if ‘‘you are writing children’s books, you need to be a ruthless killer’’. The identity of the character in Harry Potter and the Order of the Phoenix has been kept a secret until the book is published on Saturday.

In an interview with the BBC, she said about killing off her character: ‘‘Well I had written the death, re-written it and that was it. It was definitive. And the person was definitely dead. And I walked into the kitchen crying and Neil (her husband) said to me ‘What on earth is wrong?’ and I said ‘Well I’ve just killed the person.’’’

Even her husband does not know who the doomed character is and Rowling stoutly defended the secrecy surrounding the plot.