Quietly, ingeniously and, of course, cryptically, the beloved – and sometimes feared – crossword setter Araucaria has used one of his own puzzles to announce that he is dying of cancer.

The Rev John Graham, who takes his pseudonym from the Latin for the monkey puzzle tree, told Guardian readers of his terminal illness in Friday's paper.

Above cryptic crossword No 25,842 sat a set of special instructions: "Araucaria," it said, "has 18 down of the 19, which is being treated with 13 15".

Those who solved the puzzle found the answer to 18 was cancer, to 19 oesophagus, and to 13 15 palliative care. The solutions to some of the other clues were: Macmillan, nurse, stent, endoscopy, and sunset.

Speaking from his home in Cambridgeshire, Araucaria said this particular puzzle had not taken him very long, adding that a crossword had seemed the most fitting way to make the announcement.

"It seemed the natural thing to do somehow," he said. "It just seemed right."

That said, he has no plans to refer to his illness in future puzzles: "I should think this is a one-off because I don't really know what else there will be to say."

The 91-year-old said he was very pleased that his doctors had decided against surgery or chemotherapy – two prospects he had been dreading. Exactly how long he has left, however, remains something of a mystery. "There isn't a prognosis, really," he said. "They simply don't know how long it's going to take. I asked them last week how long I'd got, but nobody knows how long you've got! They said it won't be years and years, but it could be a large number of months."

Araucaria said he had been very touched by the reaction to the crossword, which first appeared in the puzzle magazine 1 Across. "People have been ringing and sending me cards," he said. "It's been very nice, but I can't reply to them all."

Worried, perhaps, that he had appeared immodest, he was quick to add: "I don't mean that I've been inundated with them but I've had a nice number."

For as long as he can, Araucaria intends to carry on conjuring up several puzzles a month – just as he has for more than half a century. After all, he pointed out: "I'm not actually doing much else." Three more puzzles are scheduled for the Guardian this month. "I can't stick at it for quite so long but it's going all right," he said. "Someone will have to tell me if the quality's going off, but I think it's all right so far."