In Scene 3 of Sophocles's "Oedipus Rex," a messenger arrives with the news that King Polybos is dead and the people of Isthmus want Oedipus to be their king. Oedipus's joyful reaction to the news of the king's death is evidenced as he feels that it dispels the oracle's prophecy that he will kill his mother. However, Oedipus is still worried that he may marry his mother.
But, in Scene 4, Fate steps in again and produces the shepherd being brought in by servants of the house of Oedipus. As the shepherd nears, the messenger from Corinth recognizes him: "I know him, he was Laios's man."
When the shepherd fails to recognize the messenger, the messenger refreshes his memory and tells him that "you gave me a baby boy to bring up as my own." He then reveals that he gave the baby to King Polybus and his wife who had no children. "King Oedipus was once that little child." Hearing these words, Jocaste tries to intervene, but Oedipus insists on learning the truth. The shepherd admits to having given the child to the messenger from Corinth. And, upon further questioning by Oedipus, the king learns from the shepherd,
They said it was Laios's child; But it is your wife who can tell you about that.
Oedipus asks him why Jocaste gave him the baby. The shepherd replies, "It was said that the boy would kill his own father." He gave the messenger the boy because he
pitied the baby, my king,/And I thought that this man would take him far away/To his own country./He saved him--but for what a fate!/For if you are what this man say you are,/No man living is more wretched than Oedipus.
At this point Oedipus realizes, "It was true! All the prophecies!" The revelation overwhelms him with agony. Oedipus rushes into the palace damning himself for the fate that he has been unable to overcome and his tragic mistake, or hamartia as it is named in Aristotle's Poetics.