Clytemnestra never forgave Agamemnon for sacrificing their daughter and by the time Agamemnon was fighting in the Trojan War, she fell for Agamemnon’s uncle, Aegisthus.

When he returned from Troy, Agamemnon took his mistress Cassandra with him. This made Clytemnestra even more angry and she slay both Agamemnon and Cassandra with an axe. Aegisthus was Clytemnestra‘s accomplice but was later on killed in revenge by Clytemnestra's son, Orestes.