According to Smithsonian magazine, Egyptian law and tradition decreed that pharaohs marry their sisters. Cleopatra married her oldest brother after the death of her father, and she married her youngest brother after the death of her first brother.
According to Dr. Thayes Watkins of San Jose State University, Cleopatra became queen when she married her oldest brother after the death of her father. Cleopatra then remarried after the death of her brother during battle. She was married to her youngest brother until his death, after which she became the sole ruler of Egypt.
According to Saint Louis University, many believed that Cleopatra poisoned her younger brother to take the throne. She also bore the children of Julius Caesar and Marc Antony while she was married to her brothers.