Complex sentence: Most Egyptologists believed that Pothinus used his influence to turn Ptolemy against Cleopatra, and in spring of 48 BC Ptolemy, under Pothinus's guidance, attempted to depose Cleopatra in order to become sole ruler, while Pothinus planned to act as the power behind the throne.
Split into simpler sentences: Most Egyptologists believed that Pothinus used his influence to turn Ptolemy against Cleopatra. In the spring of 48 BC Ptolemy, under Pothinus's guidance, attempted to depose Cleopatra in order to become sole ruler, while Pothinus planned to act as the power behind the throne.