Frerin, the lost son of Durin's house.

Based on my tumblr, youngerbrotherfrerin.tumblr.com , where Frerin did not die in the battle of Azanulbizar, but was imprisoned along with Thrain instead and managed to escape after his father was murdered by Azog. He has been wandering the wilds ever since, refusing to return to his family who, as he believes, abandoned him, seeking revenge on the pale orc - and also being the reason for the rumors Thorin heard about his father having been seen at the border of Mirkwood.