A Song of Ice and Fire book fans will remember the valonqar prophecy from A Feast for Crows, which stated that Cersei would have only three children, be replaced one day by a younger and more beautiful queen, and be killed by her valonqar, a.k.a. younger brother.
Many readers have assumed that Tyrion would be the younger brother to kill Cersei, given all the bad blood between them.
Then again, perhaps Jaime will be forced to fight back to prevent Cersei from attempting to circumvent that pesky prophecy from Maggy the Frog.
The events of the Season 7 finale may point toward Jaime in the show being the little brother to end his sister, regardless of what the books may do.