John was the youngest of the four sons of Erard II , Count of Brienne , and Agnes of Montfaucon . He seemed " exceedingly old ... about 80 " to the 14 @-@ year @-@ old George Akropolites in 1231 ; if Akropolites ' estimate was correct , John was born around 1150 . However , no other 13th @-@ century authors described John as an old man . His father referred to John 's brothers as " children " in 1177 and mentioned the tutor of John 's oldest brother , Walter III , in 1184 ; this suggest that John 's brothers was born in the late 1160s . Modern historians agree that John was born after 1168 , probably during the 1170s .