Julius Caesar uttered the phrase "Et tu, Brute?" in response to his friend and protégé Marcus Brutus during his assassination on March 15, 44 BCE, known as the Ides of March. As Caesar was attacked by a group of conspirators in the Senate, including Brutus, his astonishment at Brutus’s betrayal became iconic. This famous line, often interpreted as a plea for friendship and trust, highlights the personal betrayal he felt, as Brutus was seen as a close ally. The phrase symbolizes the theme of betrayal in politics and has pervaded literature and culture throughout history.