Iron Man and the rest of the heroes fight to save San Francisco from falling into the ocean after the Red Hulk and the Hulk's battle activated the San Andreas fault line. The Hulk goes to fight the Red Hulk again, when Thor arrives. A-Bomb explains to Thor that the Hulk needs to defeat the Red Hulk himself, for himself.
Thor not know A-Bomb, but A-Bomb knows Thor. Thor is god. Thor is greatest warrior. This is Hulk's fight. Hulk has to win for Hulk. Thor understand?
--A-Bomb
The Hulk manages to outsmart the Red Hulk, because the madder the Red Hulk gets, the hotter he gets, and literally burned himself out. After the battle, Thor tells the Hulk that he is someone that he would gladly call his friend.
I was away during a dark time. Where friend turned against friend, brother against brother. I have learned that you stood against the world. And now I believe that it had to have been with good reason. Your fight comes from within. Within your heart. Thou art someone I would be proud to call my ally.
--Thor Odinson
After everyone leaves, Doc Sampson and Thunderbolt Ross show up and tell the unconscious Red Hulk that they gave him everything he needed to kill the Hulk, but he failed, revealing that they were behind the Red Hulk all along, but we still don't know the Red Hulk's identity.