|SOME NOTES ON MEDIEVAL ENGLISH GENEALOGY|
Volume 6, page 471:
He [John de Bohun, Earl of Hereford and Essex (d. 1335/6)] m., 2ndly, Margaret, da. of Ralph (BASSET), LORD BASSET of Drayton, by Joan, da. of John (DE GREY), LORD GREY of Wilton.
John and Margaret were married before 11 Kalends of March [19 February] 1331, when the bishops of Lichfield and Coventry and of London were ordered to hear a cause concerning their marriage, the couple having discovered that they were related in the fourth degree.
[Douglas Richardson pointed out this evidence in January 2002, and Nat Taylor provided the details, citing Calendar of Papal Letters, vol. 2, p. 349.]