Board Thread:Naruto Gaiden/@comment-3279282-20150504200737/@comment-26327308-20150518140539

Its likely shisui seeing as how his body was still missing during kabutos search for edos. He is the only other uchiha alive who we know cared about itachi and isnt part of fugakus household. He also had his eye ripped out of th esocket which would explain the stiches and he would be around the age depicted (3-5 years older than sasuke)