Osbert was first mentioned in the historical record between 1121 and 1128 when he appears in a charter , which although likely a forgery , probably contains an authentic witness list . This document lists him as " Osbert archdeacon " , which means that he probably held the archdeaconry of Richmond . He was the nephew of Thurstan , who was Archbishop of York from 1114 to 1140 . Presumably he owed his position as archdeacon to his uncle and was probably appointed at a young age . A charter of Thurstan 's , dating to around 1138 , names Osbert explicitly as Thurstan 's nephew .