The drowning king - Emily Holleman

It's the dawning of a new era for Alexandria and Cleopatra and her younger brother, Ptolemy are established on the throne. Long overlooked by his father in favor of his beguiling sister, eleven-year-old Ptolemy is desperate to assert himself as a man and as a king. But he and his advisors are no match for Queen Cleopatra, who's quick to establish her primacy throughout the land, from Alexandria to Upper Egypt.

When, a year later, Cleopatra alienates Rome's remaining legions and flees the palace, Ptolemy finally gets his first taste of power, though not without its complications: Cleopatra has joined forces with their sister Arsinoe in Egypt, and Ptolemy must prepare to meet their army head-on and prove his ruthlessness to Caesar. Despite mounting doubts about where her sister's loyalties lie, Arsinoe has remained faithful to her. But when news comes that Cleopatra has manipulated Caesar to regain the throne and embraced Rome's dominance, Arsinoe is torn between her warring siblings and sensing her own nascent hunger to lead rising within.

Arsinoe must choose whether it will be her dear sister or brother she irrevocably betrays . . . and make a decision that will determine the fate of a kingdom, and all the future of history.