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  == Character background ==
  Cersei is the only daughter and first child of Tywin Lannister and his wife, Joanna; her twin brother, Jaime, was born soon after Cersei. Cersei and Jaime looked so similar as children that Cersei occasionally wore Jaime's clothes and was mistaken for him.
  The twins experimented sexually at an early age but were discovered by a servant, who informed their mother. Joanna tasked a guard to keep the twins separated and kept the matter a secret from their father, threatening the twins that she would inform him if they ever repeated it.
  Soon afterward, Joanna died giving birth to the twins' younger dwarf brother, Tyrion. Cersei blamed Tyrion for Joanna's death and started to abuse him as a baby. Martin said in ''Rolling Stone'':
  From the time she was very young, Tywin hoped his daughter would marry Rhaegar Targaryen, and he rejected the Princess of Dorne's proposal to betroth Oberyn Martell and Elia Martell to Cersei and Jaime, respectively. Cersei became infatuated with Rhaegar; feelings she hid from her brother as her father advised her.
  At the age of 11, Jaime was sent away to serve as a squire for Lord Sumner Crakehall. A year later, Aerys Targaryen rejected the proposal that Cersei marry his son, humiliating Tywin. Tywin took Cersei to King's Landing and, in the following years, refused every offer of marriage for her. In 281 AC, when Cersei and Jaime were 15, Jaime, newly knighted on the battlefield and on his way to Casterly Rock, came to King's Landing to visit his sister, from whom he had been separated for four years. She informed Jaime that their father planned to marry him to Lysa Tully and persuaded him to join the Kingsguard in order to be near her, after the twins had slept together for the first time. Thus started an affair that continued throughout Cersei's marriage to Robert Baratheon.
  While she was initially happy about marrying Robert, he didn't return Cersei's affections and repeatedly cheated on her. She then resumed her incestuous affair with Jaime, resulting in the births of Joffrey, Myrcella, and Tommen.
  During her teenage years, believing that her betrothal to Rhaegar would soon be announced, Cersei brought her companions Melara Hetherspoon and Jeyne Farman to a witch named Maggy the Frog. Jeyne was instantly frightened and left the tent. Cersei and Melara stayed and tried to get the witch to tell them a prophecy. In the face of Cersei's threats, Maggy agreed to answer three questions. In response to those questions, Maggy told Cersei she would marry the king and not the prince, that she would be overthrown by a younger and more beautiful queen, that Cersei's children would die during Cersei's lifetime, and that the ''valonqar'' (High Valyrian for "little brother") would come to end her life.
  Melara then asked if she would marry Jaime; Maggy answered that Melara wouldn't marry anyone and would die that night. It is implied that Cersei killed the girl to prevent her from speaking of the prophecies and for having ideas above her social status. Cersei spends her entire adult life attempting to subvert the prophecy and develops a strong paranoia, which eventually causes the prophecy to come to fruition.