In one novel I read years ago (probably now out of print, can't remember author, can't find it by title listings in my state's catalog of library materials), Robin was in the Crusades serving alongside with his neighbor, Lady Marian's father. When he and she caught up with each other after his return, Robin was able to tell her that her father had died in a/n heroic way. Can't recall ever reading why Robin came back instead of staying to fight, though. Also, Robin's being with Richard in the Crusades seemed to explain why Richard recognized Robin when they met again in England. Presumably Robin was fairly young (squire-age, maybe? possibly squire for Marian's father?) when they left England and Richard had seen him grow into manhood in the Holy Lands.