The family was descended from the 12th-/13th-century Welsh magnate and dynastic founder Ednyfed Fychan.
[1] Gwilym ap Gruffydd married back into the Tudors line, through Morfudd ferch Goronwy, the daughter of Goronwy ap Tudur, head of the Tudors of Penmynydd and a distant kinsman of Gwilym.
[2] Unlike his other family members, he had avoided becoming involved in Owain Glyndŵr's revolt, but lent his support in 1402.
He remarried in 1405, to Joan, a daughter of Sir William Stanley from Hooton, Cheshire.
[2] By the end of his life, Gwilym ap Gruffydd's lands in Anglesey and Caernarfonshire were generating an income of more than £112 per year.