Arsinoe IV was possibly the fourth daughter of King Ptolemy XII. She was born around 63 BC and was the half-sister of Cleopatra VII.
When Ptolemy XII died in 51 BC, his daughter Cleopatra and his eldest son Ptolemy XIII became the joint rulers of Egypt. The brother-sister married each other overlooking Arsinoe who was around 15 years of age at that time.
Arsinoe and Cleopatra had their own differences. Eventually, Arsinoe won over Ptolemy, and Cleopatra was forced to flee Alexandria.
Arsinoe seized this golden opportunity and proclaimed herself to be the queen of Egypt.