Original: After Caesar's assassination, Antony formed an official political alliance with Octavian (Augustus) and Marcus Aemilius Lepidus, known to historians today as the Second Triumvirate.
Simplified: The triumvirate broke up in 33 BC and the disagreement turned to civil war in 31 BC, in which Antony was defeated by Octavian at the Battle of Actium and then at Alexandria.