Explanation

Gavrael held Gideon's eyes. He could see that his brother was shocked at what he had just revealed. Well, of course he would be. He had not given any indication that he was any different since he stepped back into the Under Lands.

Gideon had hidden himself so damned well back then that Gavrael took years to realize that his brother did not actually leave him that time, hoping that he would die. He was actually hidden and was still protecting him, making sure he would not get killed by those monsters.