Despite his discomfort at the circumstances leading to Cersei's coronation, Jaime remains loyal to his sister, with Daenerys Targaryen and her forces sailing on Westeros. Cersei agrees to marry Euron Greyjoy after the war against Daenerys is won, but continues her relationship with Jaime, no longer attempting to hide their intimacy from their servants. Jaime negotiates with Randyll Tarly to pledge allegiance to the Lannisters, and with the help of House Tarly's forces he leads the Lannister army to defeat the Tyrell army at Highgarden. The Tyrell family matriarch, Lady Olenna, had defected to Daenerys following Cersei's role in the death of the other Tyrells. In the aftermath of the battle, Jaime allows Olenna a painless suicide-via-poison, rather than the torturous death Cersei had ordered. Before dying, Olenna reveals she was responsible for poisoning Joffrey.