RDCR07
Not a bad guy (Whale Killer)
I thought it was pretty straightforward that the Hound himself was going to come for the Mountain?I wouldn't read too much into Tyrion staring at the door. With the previous conversations he had with Dany about her succession, it's easily explainable for him to be there and thinking about a possible future with Jon/Dany kids in it. Nothing has ever pointed towards him knowing anything more about Jon (or Dany for that matter), nor is there time enough for him to have switched alliance during his meeting with Cersei.
I'm more intrigued by the Hound's "you know what's coming for you" to the Mountain.