Though their rivalry is heavily hinted in the show, the Hound and the Mountain have only really been together onscreen once. Game of Thrones is already at its last leg, and Rory McCann (the Hound), is still hopeful that we'll see a final showdown between Sandor Clegane and his undead brother.
Talking to Den of Geek, McCann says:
"I've heard of this Cleganebowl. Bring it on! I've met [Hafþór Júlíus Björnsson, who plays The Mountain] a couple of times and he's a big boy, I think I'd be the Jack Russell sort of [growls and mimes dodging about] so yeah. It'd be interesting if it happened."
A huge part of the Hound's character is his experience with his brother who burned his face when they were children. This resulted in a bitter rivalry between the two, and the Hound's crippling fear of fire.
Despite all that, Sandor Clegane has proved himself a noble man, and a lot of fans have been very pleased watching his progress throughout the show. He started out as being one of the top fighters for the Lannisters and steadily grew into the grumpy sympathetic Hound that we love today.
As of now, the future of the Hound and the Mountain are unclear, but hopefully David Benioff and D.B. Weiss have something great planned for the last season.
Game of Thrones 8 is set to come out either in 2018 or 2019.