Here at A Song of Ice and Fire and “Game of Thrones” theories, we’ve already detailed two very important theories: First, Robert Strong is actually the Mountain’s reanimated corpse; and second, that The Hound is actually the gravedigger.
In other words, both Clegane brothers (Sandor “the Hound” and Gregor “the Mountain“) are actually alive — even though they have “died” — either explicitly or implicitly. Both theories are pretty convincing, and it’s not hard to imagine both of them being true.
So what is Cleganebowl?
If both Cleganes are in fact alive, then George R. R. Martin undoubtedly kept them alive for a reason. The Mountain — presumably now known as Robert Strong — was Frankenstein-ed for seemingly one purpose and one purpose only: To protect Cersei.
Cersei is being put to trial by the Faith, and she has chosen Robert Strong as her champion. In other words, he will duel to the death. If he loses, Cersei is guilty. If he wins, Cersei is innocent.
Since Cersei chose “trial by combat” as her guilty-or-not-guilty measuring stick, that means the Faith has to choose a champion as well. That’s where the Hound comes into play.
If the Hound is indeed the gravedigger, that means he is currently on Quiet Isle, home of those sworn of the Faith.
“Why do they call it the Quiet Isle?” asked Podrick.“Those who dwell here are penitents, who seek to atone for their sins through contemplation, prayer, and silence. Only the Elder Brother and his proctors are permitted to speak, and the proctors only for one day of every seven.”–A Feast for Crows, Brienne VI
We hear that the Hound “died” on Quiet Isle, but the Elder Brother (essentially the leader of Quiet Isle) likens coming to Quiet Isle and swearing faith to the Seven as a “rebirth” — and in order to be re-born, one must “die” first. That’s a crucial point to the “the Hound is the gravedigger” theory. If true, it means the Hound didn’t literally die; it was metaphorical.
So this leads us back to Cleganebowl. Cersei, being tried by the Faith, has chosen Robert Strong (Sandor Clegane) as her champion. The Faith could choose their large, burly gravedigger (the Hound, or Gregor Clegane) as their champion.
Cleganebowl. Get hype.