JK Rowling explains why Harry Potter was put in a cupboard

Scene from Harry Potter and the Philosopher's Stone.

A dinner table bust up between Harry Potter's parents and his aunt and uncle sparked the Dursley's animosity towards the young wizard.

JK Rowling has finally explained why Potter's Uncle Vernon and Aunt Petunia Dursley disliked him enough to leave him languishing in the cupboard under the stairs.

She writes on her fan website, Pottermore, that the rift started when Potter's mother Lily introduced her then boyfriend James Potter to the Dursleys.

James was amused by Vernon, and made the mistake of showing it," Rowling writes.

"Vernon tried to patronise James, asking what car he drove. James described his racing broom."

She said Vernon suggested wizards must live on unemployment benefits then James explained his parents had saved a fortune in solid gold at Gringotts Wizarding Bank.

"(He) could not tell whether he was being made fun of or not, and grew angry," Rowling writes.

"The evening ended with Vernon and Petunia storming out of the restaurant, while Lily burst into tears and James (a little ashamed of himself) promised to make things up with Vernon at the earliest opportunity."

Rowling writes it is Harry Potter's likeness to his father that is behind his uncle's animosity towards him.

A Warner Brothers Harry Potter spin-off, Fantastic Beasts and Where to Find Them, will be released in November next year.

It will be the first in a movie trilogy set 70 years before Harry was born and will star Oscar winner Eddie Redmayne and Katherine Waterston.

- AAP