The Hound and the Mountain had a short but tense reunion in the final episode of "Game of Thrones" this season, and Sandor Clegane certainly made known his continued hatred and anger against his older brother.

The much speculated and anticipatedCleganebowl however did not happen but the ominous words spoken by the Hound gave GoT avid followers one thing to look forward to in the final season of “Game of Thrones.”

Sandor Clegane asked, what did they do to you?

Without waiting for an answer that was not to come given the Mountain was not really in the mood to talk even if it wanted to, the Hound continued, “doesn't matter, it's not how it ends for you, brother.

You know who's coming for you.”

But what really were the roots of the enmity between the Clegane brothers?

The Scar

Faithful followers of “Game of Thrones” TV series definitely knew the story of how the Hound had his horrible facial scar. The late Littlefinger narrated to Sansa Stark during the Hand’s Tournament in season 1, the story of how Ser Gregor Clegane, who already has a reputation for violence, caught his younger brother, one evening, playing with Gregor’s toy (a wooden knight) by the fire.

Without a word, he grabbed his brother by the scruff of his neck and pushed his face on the burning coal and mercilessly held it there while Sandor screamed in pain and his face melted.

But there is more to the story.

Apparently, their father covered up Gregor's crime by telling people that Sandor Clegane's facial injuries were caused by a bedding that caught fire.

Kinslaying

Apart from the horrible cruelty, the Mountain subjected his younger brother, there may be another equally atrocious act Ser Gregor Clegane was rumored to have committed— kinslaying or the killing of one’s family member.

In the ASOIAF first novel Game of Thrones, it was rumored the mountain was responsible for the mysterious deaths of their sister and father. King Robert Baratheon was said to be suspicious of Ser Gregor Clegane whose father died in a hunting accident leaving the House Clegane estate to him.

These crimes may have cause Sandor to loathe his brother even more.

The Mountain’s cruelty

Ser Gregor Clegane’s reputation for cruelty, murder, and rape was already widely known for he has committed countless of these acts according to the ASOIAF novels. In season 1 of “Game of Thrones,” Ned Stark ordered Beric Dondarion to bring the Mountain to the capital to face King’s justice for terrorizing the Riverlands.

The most famous acts of brutality and cold murder that the Mountain committed were the rape and killing of Raegar’s wife and children during the Robert’s Rebellion.

The Hound, despite his hardened attitude and horrible face, was proven this season to be a kind soul deep inside. He may have hated his older brother for all the wanton acts of violence he committed since they were little.

Should the Cleganebowl, finally happen in "Game of Thrones" season 8, it is up for Sandor Clegane to deliver justice to all who have brutally died and suffered at the hands of the Mountain, one of them is the Hound himself.