W E Wightman, "The Lacy Family in England and Normandy, 1066-1194", genealogical chart following p 260. (pp. 175, 177-178): ". . . all that can be said of his father John 'Monoculus' is that he was not an important member of the baronage. A measure of his respectability -- or rather acceptability in the eyes of the rest of his contemporaries -- is to be found in the marriage of his sons, Payn, a younger son, married the Lacy heiress. Eustace fitz John, Payn's eldest brother, married Beatrice, the Vesci heiress, and thus inherited through her the honours of Alnwick and Malton. . . .the sons of John 'Monoculus' were of sufficient standing to be acceptable husbands
for the daughters of major barons."
Burke's _Ext. & Dorm. Peerages_ ('BED') under ('Clavering') 121, identifies this John 'Monoculus' de Burgh as nephew & heir of Serlo de Burgh, & grandson of Eustace de Burgh.