A rabbi relates this story in a video.
A young man went over to another Jew at a wedding and said, “Do you remember me? The other man looked at him and said, “No, who are you?” The young man introduces himself and tells him that he was one of his students. “You were my student in third grade,” the man says. “It’s been a long time, what have you been doing, how are you?” Read more on my blogspot.