A filmed conversation between Neil Gaiman and Michael Chabon at the Jewish Community Centre of San Francisco, in which Gaiman reminisces about Terry Pratchett, is lovely, and sad, and funny, and well worth a look.

It covers some well-trodden ground, such as how the pair decided to collaborate on Good Omens (it was Gaiman’s idea; Pratchett asked him if he could take it on or collaborate; Gaiman said yes. “It was like Michelangelo phoning and asking if you want to paint a ceiling together”).

And it sees (around 21 minutes in) Gaiman discuss Pratchett’s “huge and noble” decision to speak out about his Alzheimer’s diagnosis. “Here’s somebody who’s fought to be taken seriously and to make people realise that you can write a serious novel, set in a fantasy context, on a flat world on the back of elephants on the back of a giant turtle floating through space and it can still be a real novel. And he’s got there,” says the novelist.

“He’s got serious critical attention and now he risks losing it. But … he announced it to the world and he used it as an opportunity to start the dialogue, to start talking about the fact that in the last 30 years we have made such incredible progress in the battle against cancer … compared to what’s gone into cancer, it’s pennies have gone into Alzheimer’s … and so Terry decided to get loud about that and to start talking about that. And then Terry, incredibly bravely, decided he wanted the right to die at the time of his own choosing, and given that that was illegal in the UK, he decided to do what he could to draw attention to it.”

There’s a reading from Good Omens, Gaiman’s first in 25 years: “It was very early on Saturday morning on the last day of the world,” he begins. Gaiman picks the delivery man passage, which includes the excellent line “They’d come here to spoon, and on one memorable occasion, fork”, as well as the much-quoted line from Death, “DON’T THINK OF IT AS DYING … JUST THINK OF IT AS LEAVING EARLY TO AVOID THE RUSH.”

My favourite moment, though, comes about 25 minutes in, when a visibly moved Gaiman decides to talk about the way he wants to remember Pratchett, and recounts a hilarious story from the pair’s tour for Good Omens, decades earlier. (He also mentions, casually, that Pratchett was writing an autobiography: anyone else ready to leap around with cautious glee in the hope that one day we might get to see it?)

“About a year ago, I’m in a car, somebody else is driving, my phone rings, and I answer it, and a voice says ‘Hello, it’s me, I’m doing my autobiography and there’s something I can’t remember, and I thought maybe you can help me with it’. And my heart welled. It’s like, Terry, you have Alzheimer’s, I will be your memory … I said ‘What is it you need to know?’,” begins Gaiman, wryly.

“He said ‘Well, you remember we were on the Good Omens author tour in February 1990’ … He said ‘We were in New York and we went to that ABC affiliate radio station, and the interviewer had not actually read the book … so when we started telling him about Agnes Nutter … we started explaining about this 17th century witch who all of her predictions were true … He did not realise this was fictional. We realised he had not read the book, and the engineers in the control room behind the glass panel who we could see and he could not, were lying on their backs kicking their legs against the walls.’

And I said, ‘Of course I remember. I was willing to let that go on for the entire interview’… He said ‘So, you remember we walked out, and then we walked down the street, and we were singing the They Might Be Giants’ song Shoehorn with Teeth’, and I’m like, ‘I will take your word for it on that one’.

He said ‘Was it 40th, 41st or 42nd Street?’. At which point I’m going, ‘You have fucking Alzheimer’s, I don’t know’. That is how I want to remember Terry.”