Research Notes:
A 1616 pedigree of the Knightley family states, "Johannes de Sancto Johanne, miles, Dominus de Plumpton in com. North'ton, jure materno" married "Matildis, filia Roberti, filij Nigelli." Their arms are described as "Gules two bars argent a canton ermine, impaling paly of six argent and gules." John is shown as the son of "Willelmus de Sancto Johanne de Hameldon" and "Sara, filia et una heredum Roberti de Plumpton." [1]
[1] Joseph Jackson Howard, ed., "Pedigree of the Knightley Family of Fawsley, Co. Northampton, compiled by Augustine Vincent, from the original in the possession of Sir R. Knightley, Bart., M.P.," Miscellanea Genealogica et Heraldica, Vol. 1 (London: Hamilton, Adams, and Co., 1868), 88-102 at 92, [GoogleBooks], [HathiTrust].