[J.K] Rowling has given it her public seal of approval: “Seeing Jim Kay’s illustrations moved me profoundly,” she wrote for the dust jacket. “I love his interpretation of Harry Potter’s world, and I feel honoured and grateful he has lent his talent to it.”

She also wrote to Kay privately. “She sent a really lovely letter, and that’s the first time it hit me that this was real,” he says. “Imagine you’re a vicar and you find a Post-it note from God on your fridge. It was like that.”

McGonagall: [Kay's partner Louise] Clark is also the model for Professor McGonagall in the new book. Kay had to age her artificially – her real hair is ringleted and blonde rather than a harsh grey – but it was helpful to have her as a basis.

Hagrid: An old biker who lives in Kettering, with the eyes of Winston Churchill. He was the first character Kay drew, and he set the viewpoint for the rest.

Mr Dursley is based on the local butcher.

Hermione is based on Kay’s niece.

Harry was a boy he spotted swinging from the bars on the London Underground, and Kay had two stops to introduce himself to the boy’s mother and persuade him to pose for him – for a book whose subject he could not yet disclose.

Draco Malfoy and Ron Weasley both came from a school in Burford, to which he’d been invited by a pupil who’d loved A Monster Calls.