Jaime killing Cersei has basically always been on the cards as it was part of the prediction she got as a girl that her younger brother would kill her and she typically always assumed it to be Tyrion despite Jaime being a couple of minutes younger too.
Newer fan theory doing the rounds is that Arya does it wearing his face. Thus killing two birds with one stone...
Newer fan theory doing the rounds is that Arya does it wearing his face. Thus killing two birds with one stone...