From the NY Times obit of John Fowles.
As much as it frustrated some of his readers, Mr. Fowles always believed he had done the right thing by leaving the endings of his most celebrated novels open-ended. But he was not above bending his own rules when the occasion called for it.
He once told an interviewer that he had received a sweet letter from a cancer patient in New York who wanted very much to believe that Nicholas, the protagonist of “The Magus,” was reunited with his girlfriend at the end of the book - a point Mr. Fowles had deliberately left ambiguous. “Yes, of course they were,” Mr. Fowles replied.
By chance, he had received a letter the same day from an irate reader taking issue with the ending of “The Magus.” “Why can’t you say what you mean, and for God’s sake, what happened in the end?” the reader asked. Mr. Fowles said he found the letter “horrid” but had the last laugh, supplying an alternative ending to punish the correspondent: “They never saw each other again."