Within hours of Caesar's murder, Mark Antony moved to grasp the reins of power.
However, Mark Antony was politically caught off guard by Caesar's will. The will named Caesar's grandnephew Octavian his heir apparent.
Mark Antony, who was twenty years Octavians' senior, decided that this eighteen-year-old boy would be a minor nuisance and would not pose much of a threat to the leadership of the Caesarean party.
When one considers Mark Antony's many years spent in Cleopatra's court, his actions in Egypt which led up to his defeat at the battle of Actium in 31 BCE, and his ultimate suicide, he was either in love with Cleopatra or she truly was a "siren" as Roman propaganda described her.
In either case, it meant that she duped Mark Antony. Regardless, the Roman Empire could not suffer by having one of its leaders under the spell of a foreign queen. Mark Antony's defeat and suicide meant Octavian would become Augustus and become Rome's first Emperor.