Augustine was in Milan when God touched his heart and changed his life. He then left his former life of license (he even had an illegitimate son). When he returned home, his former girl friend called to him: “Augustine, Augustine, it is I.” He turned and said: “Yes, but it is not I.”
Note: This story has been retold and published many times but it is wrongly connected with Augustine. Go here for more. It is a conflation of a fable (which Ambrose retells) and Augustine's conversion story. Here's the fable as retold by Ambrose: Let the man deny himself and be wholly changed, as in the fable they relate of a certain youth, who left his home because of his love for a harlot, and, having subdued his love, returned; then one day meeting his old favorite and not speaking to her, she, being surprised and supposing that he had not recognized her, said, when they met again, “It is I”. “But,” was his answer, “I am not the former I”. (Ambrose, Concerning Repentance, Book II, Ch 10.96).