to show that his rival had fallen away from conduct becoming a citizen, he had the will which Antony had left in Rome, naming his children by Cleopatra among his heirs, opened and read before the people.
Octavian and Mark Anthony were two members of the second triumvirate - an alliance which initially proved to be mutually beneficial to them. However, the relationship between Octavian and Anthony started to decline after the battle of Philippi. The brother and wife of Mark Anthony, Lucius Antonius and Fulvia, attacked Octavian and temporarily declared Anthony the sole leader of the Roman empire. Subsequently, Octavian attempted to take Anthony's province of transalpine Gaul. Anthony and Octavian then came to an agreement through the pact of Brundisium. Through this pact, Anthony married Octavia, Octavian's sister. But when Anthony went east and began his relationship with Cleopatra, he sent Octavia back to Italy. He also declared Caesarion the true heir to the Roman empire, a direct affront to Octavian. The breaking point for Octavian was the "Donations of Alexandria", a ceremony during which which the eastern provinces of Rome were distributed by Anthony to Cleopatra and her children. This demonstrated Anthony prioritizing Egypt over Rome, and by extension, Cleopatra over Octavia. This provided Octavian with material to use as propaganda to sow mistrust of Anthony in the western Roman empire. This also provided Octavian with justification to carry out the illegal act of reading Anthony's will in public.