When Did Cersei and Jaime Start Sleeping Together

When did Cersei and Jaime become lovers?

Although it has never been confirmed exactly when Cersei and Jaime began their romantic relationship, it probably began as innocent experimentation when the two were still young children.

Did Cersei sleep with her son?

When Cersei has an affair with Lancel Lannister, their cousin. Cersei sleeps with their cousin Lancel throughout seasons one and two. Lancel does everything she asks him to, including causing the death of King Robert. In season five, Lancel confesses the affair and the death of Robert to the High Sparrow.