J. K. Rowling has finished writing her latest book.

Away from the 'Harry Potter' series she created, Rowling's 'Comoran Strike' crime novels - which she published under the pseudonym Robert Galbraith - have proven to be very popular and she has now announced on her Twitter feed that the fourth instalment in the series titled 'Lethal White' will be out before the end of the year.

Referencing a small bird finding its way into her home and her scriptwriting commitments for the 'Fantastic Beasts' films, she tweeted: ''Strike no. 4 is finished and will be out later this year. I'm currently writing about 'Fantastic Beasts', so the little visitor in last tweet was appropriate!''

The novels - which also include 'The Cuckoo's Calling', 'The Silkworm' and 'Career of Evil '- centre around the adventures of a private investigator named Strike and his assistant Robin Ellacott as they work their way through a number of criminal cases.

When a fan quizzed her about the plot for the 4th book in the series - which was recently turned into a BBC One drama - Rowling was staying tight-lipped on any spoilers.

She said: ''I don't want to spoil your enjoyment/continuing frustration. #LethalWhite [sic]''

Although Rowling, 52, has managed to diversify her writing career she has admitted that she found it hard to live up to the huge success of the 'Harry Potter' franchise.

She revealed: ''There was a phenomenal amount of pressure that went with being the writer of Harry Potter, and that aspect of publishing those books I do not particularly miss. So you can probably understand the appeal of going away and creating something very different, and just letting it stand or fall on its own merits.''