Cassandra or Kassandra (; Ancient Greek: Κασσάνδρα, pronounced [kas:ándra], sometimes referred to as Alexandra; Ἀλεξάνδρα) in Greek mythology was a Trojan priestess dedicated to the god Apollo and fated by him to utter true prophecies but never to be believed. In modern usage her name is employed as a rhetorical device to indicate a person whose accurate prophecies, generally of impending disaster, are not believed. Cassandra was a daughter of King Priam and Queen Hecuba of Troy. Her elder brother was Hector, the hero of the Greek-Trojan War.
https://en.wikipedia.org/wiki/Cassandra