Ptolemy X Alexander I was the son of Cleopatra III and Ptolemy VIII Euergetes II Physcon. His mother was married to Ptolemy VIII while her own mother was still his official wife. Cleopatra III bore two sons - Ptolemy IX Philometor Soter II (Lathyros) and Ptolemy X Alexander I and three daughters, Cleopatra IV, Cleopatra Tryphaena, and Cleopatra Selene.
Upon the death of Ptolemy VIII, his will left the succession of the Egyptian throne to Cleopatra III and to whichever son she preferred. Cleopatra III actually hated Lathyros and preferred Ptolemy X Alexander, the youngest of her two sons. Unfortunately, the citizens of Alexandria preferred Lathyros to be co-regent. At the time, Lathyros was the governor of Cyprus and he was summoned back to Alexandria to become co-ruler with his mother (106-101 BC). Ptolemy X Alexander I was then sent to Cyprus in Lathyros' place in 113 BC.
Lathyros' marriage to sister Cleopatra IV, was annulled by his mother and he was married to his youngest sister Cleopatra Selene. Cleopatra IV fled to Cyprus where she tried to raise an army and marry her other brother Ptolemy X Alexander. When her effort to marry her second brother failed, she fled to Syria where she used her army as a dowry and married Antiochus IX Cyzicenus who was son of Antiochus Sidetes and Cleopatra Thea.
Cleopatra III never changed her mind and eventually succeeded in discrediting Ptolemy IX in 107 BC by accusing him of trying to murder her. Ptolemy IX Lathyros was then forced to flee back to Cyprus leaving his wife and his two sons behind . It was at this time that Ptolemy X Alexander was summoned by his mother back to Alexandria from Cyprus and assumed the throne.
Ptolemy X Alexander I ruled Egypt jointly with his mother Cleopatra III until her death five years later in 101 BC. Still the popularity of Ptolemy X Alexander never materialized. Eventually he was driven from Egypt by his own subjects and died in a naval battle, or possibly murdered, in 88 BC. Lathyros was brought back to Alexandria to try to put back together the Ptolemaic Empire. He died at the age of 62 in 80 BC leaving no legitimate heir to the throne, which then passed to his daughter Cleopatra Berenike who ruled alone briefly before Ptolemy XI, son of Ptolemy X Alexander, was obliged to marry his stepmother. Just 19 days after the marraige, Ptolemy XI murdered his new wife enraging the people who them stormed the palace and killed him.