When first talking about the impact of his Alzheimer’s disease to The Guardian in March 2008, Terry Pratchett commented that his “fiction – be it for adults or children – isn’t just comic  … You can’t laugh all the time. There’s humour in the darkest places. I mean, The Lord of the Rings is a dark book. There’s an Arthurian darkness – we can fight evil, but ultimately we die.” He recalled Rosemary Sutcliff’s book Sword at Sunset, about Arthurian Britain.

Her marvellous idea was that King Arthur and his warriors were effectively the last Romano-Britons fighting against the dark forces. And you’re going to lose, but you have to go on fighting. Something like that you can add humour to. And that’s what I’ve tried to do.