This could go one of two ways.
An Egyptian Pharaoh decides it's time to choose his heir's queen. Because the bloodline must be kept pure, he must choose one of his daughters. His eye falls on his youngest daughter because like the Pharaoh to be, she is one of his healthier offspring, and she is also intelligent and well spoken.
The young princess always had a close relationship with her eldest brother, and never dreamed she would be chosen to marry him; it was more likely to be one of her older sisters. She is surprised and upset when given the news. He's her big brother.... But she'll be surprised when after the wedding her feelings toward him start changing.
A young thief decides to risk stealing a pomegranate from the royal garden. He never noticed that the Pharaoh was nearby. When caught, the Pharaoh decides to make the boy his pleasure slave.