Thyestes had been fighting with his brother, Atreus, for the throne of Mycenae for some time, as well as having an affair with Atreus' wife, Aerope. In vengeance for the affair, Atreus killed Thyestes' first sons and served them to him at a banquet. Thyestes swore vengeance.
An oracle then advised Thyestes that, if he had a son with his own daughter, Pelopia, that son would kill Atreus. Thyestes did so and the son, Aegisthus, did kill Atreus. However, when Aegisthus was first born, he was abandoned by his mother, ashamed of her incestuous act. A shepherd found the infant Aegisthus and gave him to Atreus, who raised him as his own son. Only as he entered adulthood did Thyestes reveal the truth to Aegisthus, that he was both father and uncle to the boy. Aegisthus then killed Atreus.
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