As a young Neapolitan nobleman he caught a nasty skin disease. Unable to take part in worldly vanities, he became ordained when it started to clear up.
Then he received a mysterious letter proposing he should come and help with a new religious order. In a bizarre twist of fate, this was actually a case of mistaken identity. The letter bore his name but a different address.
He never noticed and took up the appointment. He was made a superior and did pretty well.
But if people took notice of him, he would fall to his knees and hold up a crucifix shouting: "Look at him — not me!" We expect his skin was still a bit blotchy and embarrassing.