Always wondered why the Dursley's disliked Harry Potter so much? Enough to keep him in a cupboard under the stairs? Well, J.K. Rowling has finally unveiled the story behind the Potter-Dursley feud.

On Tuesday, interactive sections of the final book in the series, The Deathly Hallows, were released on the official fan website Pottermore, alongside the origin of Uncle Vernon and Aunt Petunia's names and details of their relationship with Harry’s parents James and Lily.

Long before the boy wizard was born, when Petunia accepted Vernon Dursley's proposal for her hand in marriage - "very correctly, on one knee in his mother’s sitting room, Petunia accepted at once." - there was one snag that kept the bride-to-be from feeling over the moon: "The fear of what her new fiancé would make of her sister, who was now in her final year at Hogwarts School of Witchcraft and Wizardry."

"Vernon was apt to despise even people who wore brown shoes with black suits; what he would make of a young woman who spent most of her time wearing long robes and casting spells, Petunia could hardly bear to think," reads the extract.

A meeting of the muggles and wizards was arranged at a restaurant but things quickly turned sour and "the relationship nose-dived from there".

"James was amused by Vernon, and made the mistake of showing it," writes Rowling. "Vernon tried to patronise James, asking what car he drove. James described his racing broom."

Vernon then voiced his presumptions that wizards must have to live on unemployment benefit, which caused James explain the wizard's bank Gringotts, and the fortune of solid gold his parents had saved there.

"Vernon could not tell whether he was being made fun of or not, and grew angry. 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."

J.K. Rowling unveils new backstory on how the Dursleys fell out with the Potters