a. The earliest documented member of the Thweng(e) family, Robert de Thwenge, styled Robert Fitz Robert, is recorded in 1166 as holding a knight's fee of the old feoffment of William de Percy. Some believe the family origins were in Durham, with a relationship to the Fitz Marmadukes, Lords of Horden. It appears likely that their name came from Thwing, located in East Riding, Yorkshire.