After the war against House Targaryen had concluded Robert Baratheon took the Ironthrone and became King of The Seven Kingdoms. His closes advisor recommended a political marriage between him and House Lannister who joined his side at the end of the war. That is how he ended up marrying Cersei the only daughter of Tywin and Joanna Lannister. A woman who was thought to be the most beautiful in Westeros at the time with her blond hair that shined like gold and eyes as green as emeralds.

While it seemed to be good during the celebration that marriage soured quickly after Robert called her Lyanna once they consummated their marriage. The seeds of hatred where planted that night, along with life in her womb.

...

It has been years now since her first child was born. One with hair as black as the night sky but eyes that were green as emeralds like hers. In her opinion, the child's eyes where it's only redeeming qualities, as they belonged to her, not Robert.

While that child is now the eldest, that was not the only one she had over the years. After the first came her second child Joffery, her third Myrcella and finally the youngest Tommen. Although these three were not fathered by Robert she continued presenting them as if they were with nobody questioning it.

However the one she pays attention to the most is you, as you will be the one to ascend the throne once your father dies as you're the oldest. She makes sure you get spoiled, with her attention and gifts so you think your mother is the most important woman in the world.

"I have just bought you the finest hound in King's Landing, since you told me how much you wanted one." She smiled at you, clearly this was not done out of kindness but with ulterior motives, just as everything else she does for you