To mark Halloween for Harry Potter fans, J.K.Rowling has revealed her least favourite character in the series and it's not Voldemort. 

At the end of a 1,700-word new story published today on Pottermore - the website that allows fans of the boy wizard to dip into the wizarding world after the conclusion of the books and films - Rowling writes, "Dolores Umbridge is one of the characters for whom I feel the purest dislike".

"Her desire to control, to punish, and to inflict pain, all in the name of law and order, are, I think, every bit as reprehensible as Lord Voldemort’s unvarnished espousal of evil."

She also reveals the real-life person who inspired the infamous character who forces Harry Potter to cut the words "I must not tell lies" into to his hand.  

Though she does not disclose the identity of the figure, she explains she had been her teacher "long ago ... in a certain skill or subject" and describes her as a person "whom I disliked intensely on sight".

"The woman in question returned my antipathy with interest. Why we took against each other so instantly, heartily and (on my side, at  least) irrationally, I honestly cannot say."

Rowling continued, noting the woman’s "pronounced taste for twee accessories", including "a tiny little plastic bow slide, pale lemon in colour", which the novelist felt was more "appropriate to a girl of three".

Dolores Umbridge first appears in Harry Potter and the Order of the Phoenix, the fifth book in the series, where we meet her as Senior Undersecretary to the Minister for Magic, before she takes over teaching Defence Against the Dark Arts at Hogwarts and later appoints herself as headmaster of the school in Professor Dumbledore's absence. 

Today's new release from Rowling also discloses for the first time that Umbridge is a half-blood, the daughter of a wizard and a Muggle (non-magical person), where in the books Umbridge boasts about her 'pure-blood' credentials. 

The essay about Dolores Umbridge is just one entry in over 5,500 words of new writing by J.K. Rowling posted on Pottermore at Halloween to mark the launch of an interactive version of Harry Potter and the Order of the Phoenix on the website.

Other entries include a look at the magical and mysterious creatures Thestrals, the dark history of the wizarding prison Azkaban, thought on the character Sybil Trelawney, details of all who have held the position of Minister for Magic and an introduction to the ancient wizarding practice of Naming Seers.