I found this out from lurking on r/freefolk.
In a new interview, Jonathan Pryce gives away that:
"When Cersei's trial happens.... High Sparrow and everyone else is waiting in the Sept of Baelor for Cersei to show up. And the High sparrow is very certain for Cersei to show up and so is everyone else. No one expects that something very unpleasant is about to happen".
this spoiler gives credence to the rumors that Cersei kills the Tyrells, High Sparrow and a lot of the Faith Militant in the season finale with wildfire. people are speculating that this scene will be like the Red Wedding. The doors to the Sept of Baelor will be locked and while everyone is waiting for Cersei, Qyburn will blow the entire place up with wildfire.
this info was translated from this SOURCE