Pelopia
Pelopia was the daughter of Thyestes. After Atreus murdered her younger brothers and served them up as stew, Thyestes received a prophesy that he could revenge himself on his brother by getting a son on his own daughter, the unfortunate Pelopia.
Pelopia, whether willingly or no, bore her father a son, Aegisthus, but so appalled was she at the situation that she abandoned him on a hillside. He was found by a shepherd who delivered him to Atreus himself, and Atreus raised him to manhood.
When the truth came out and Aegisthus was identified as both son and grandson of Thyestes, and both son and brother of Pelopia, Pelopia killed herself out of shame.