Nietzsche was famously close to Richard Wagner for a time before splitting from him and subsequently heaping much scorn upon him. Most accounts of their relationship have focused on things like Wagner being a disciple of Schopenhauer, as Nietzsche was early in his life, thus making their split inevitable when Nietzsche became disenchanted with Schopenhauer’s philosophy. Or they mention that Wagner was the same age as Nietzsche’s father, who died when he was only five, thus making Wagner the father-figure that Nietzsche had to rebel against for his own intellectual independence. You get the picture. Serious issues of philosophy and psychology here.

But as it turns out, uh… oh, let’s let Peter Watson tell it:
Only nine days after the composer’s death in 1883, Nietzsche confided in a letter to a friend, “Wagner was by far the fullest human being I have known.” However, he went on, “Something like a deadly offence came between us; and something terrible could have happened if he had lived longer.”
Details about this “deadly offence” emerged only in 1956, when correspondence first came to light between Wagner and a doctor who had examined Nietzsche. It related to a consultation Nietzsche had in Switzerland in 1877. The doctor, a passionate Wagnerian, examined Nietzsche and found his health poor—indeed Nietzsche was at risk of going blind. This was when Nietzsche and Wagner were still friends and so, following the examination, Nietzsche wrote to Wagner, reporting the diagnosis, but also enclosing an essay on The Ring, which the doctor had written and given to Nietzsche, on the understanding that it would be passed on. Wagner replied to the doctor, thanking him for the essay, but also raising the matter of Nietzsche’s health, apparently referring to the belief, common at the time, that blindness was caused by masturbation. The doctor, in his reply to Wagner, behaved extremely unprofessionally, confiding that, during his examination, Nietzsche told him he had visited prostitutes in Italy “on medical advice.” (This was sometimes recommended then as treatment for chronic masturbation.)
Even at this distance, the set of events is shocking; how much worse it must have been then. It is now known that the details of this exchange circulated during the Bayreuth Festival of 1882, coming to Nietzsche’s own notice later that same year. He confessed in a letter that an “abysmal treachery” had got back to him. More than one observer has concluded that this episode helped to unbalance Nietzsche.
It is a story that diminishes two great men.
Diminishes? Not at all! I find it amusing and deeply humanizing to realize that even two towering cultural figures like this could be brought low by the same pettiness that plagues high schools everywhere. (I haven’t read Julian Young’s biography of Nietzsche yet, but I understand that in his account, there may have also been implications of homosexuality in that letter.) I can totally see Nietzsche lying in bed on his back, feet up against the wall, arm across his eyes, a phone pressed to his ear: “…and then he told everyone at the party!! I know, right?! And after I totally dedicated my first book to him and his crappy music! God, I was so stupid, stupid, stupid! Why was I even born?!” Meanwhile, a Coldplay playlist repeats itself on iTunes. Nearby, we see a yearbook open to Wagner’s picture, now sporting devil horns, blacked-out teeth, lightning bolts above his head, and disembodied penises hovering in and about his mouth and ears.