Lucian Freud’s final portrait is of a naked man and a dog. It is unfinished but otherwise betrays no sign of the agedness of its creator, who died last July 20, halfway through his 89th year. The scale is big, a square canvas of about five feet by five feet, and the brushwork is as sure and layered as in any painting he had ever done—smooth and free around the man’s shoulders, crusty and impastoed along the arms. The palette is Caucasian-fleshy from afar but remarkably varied and intricate up close: purples and greens in the man’s legs, vivid streaks of yellow in his right hand, rust and blue at the naughty bits.

For the last 57 years of his life, Freud painted standing up rather than sitting down; the physical restrictions of seated painting, he said, had begun getting him “more and more agitated” in the 1950s, so he kicked the chair away. Painting on his feet required extraordinary stamina, given Freud’s self-imposed work schedule: a morning session with one model, an afternoon break, and an evening session with another model, seven days a week, all year round. What’s more, these sessions had a tendency to stretch on: a deliberate worker, Freud took 6, 12, 18 months or longer to complete a painting, marathoning into the night if the mood struck. But he had stamina in spades. Painting was his workout; he took no other exercise, and yet photographs of him working shirtless in 2005, when he was 82, show him to be lean and all sinew, a jockey-size Iggy Pop.

But by June 2011, Freud recognized that his body was finally failing him, and that he had only so many brushstrokes left. The naked man in the portrait was completed, but the dog, a tan-and-white whippet, would never get its hind legs. Freud prioritized its head and face, adding a little dart of terre verte (“green earth”) mixed with umber to depict the tip of the animal’s pricked-up right ear. In early July, Freud was addressing the painting’s foreground: the folds and ripples in the sheet that covered the low platform upon which his two models sprawled. Here and there, as his energy permitted, he applied quick strokes of flake white, a thick, lead-heavy paint, to the lower part of the canvas.

That was as far as he got. Able to stand no longer, he at last retired to his bedroom, one floor up from the studio he kept in his Georgian town house in West London. As he lay in bed, friends and family gathered to pay their respects. There were many visitors from both categories. Freud had an otherworldly magnetism that his intimates struggle to put into words. Deborah Cavendish, the Dowager Duchess of Devonshire, once ascribed to him “a sort of starry quality … an extraordinary sort of mercurial thing. He’s like something not quite like a human being, more like a will-o’-the-wisp.” Over the course of his life he fathered 14 acknowledged children with six women. Among his nine daughters are the fashion designer Bella Freud and the novelist Esther Freud. Two weeks into their bedside vigil, he was gone.

Freud’s was not one of those postscript deaths, the final headline in a life that had long ago ceased to matter or progress. It was an interruption—the ultimate inconvenience for a man who still had plenty of work to do and plenty of people who wanted to see his work. The restaurateur Jeremy King, who was more than a hundred sittings into an uncompleted etching when Freud died—having already sat for a painting completed in 2007—recalls that the artist “never came to terms with the fact that he was slowing down. He constantly said, ‘What’s wrong with me?’ And I’d say, ‘Well, Lucian, you’re actually much more active than any other 68-year-old I know, let alone 88.’ And the moment he lifted his hands, most of his ailments seemed to melt away. The concentration and the adrenaline pushed him through.”