Gruffydd ap Ieuan is of importance for two other reasons. With the bard Tudur Aled (q.v.) he was called upon to assist at the first Caerwys eisteddfod ( 1524 ) in the grading of bards and musicians ; the two sat with three commissioners, viz. Richard ap Howel ap Ieuan Fychan of Mostyn (father-in-law of Gruffydd ap Ieuan ), Sir William Gruffydd ( Griffith ) of Penrhyn (father-in-law of Thomas Mostyn , son of Richard ap Howel ), and Sir Roger Salusbury of Llewenni . A second reason for his importance is the fact that his nephew, or ‘great-nephew,’ bishop Richard Davies ( 1501? - 1581 ) (q.v.) , says that he remembers seeing in the possession of Gruffudd ap Ieuan (it is William Salesbury who identifies the ‘hen ewythr’ as Gruffudd ap Ieuan ) a manuscript translation in Welsh of the Pentateuch ; for details see the book by D. R. Thomas which is generally referred to under the short title of Davies and Salesbury . The manuscript which D. R. Thomas prints in this work, is, however, not the ‘lost’ translation of the Pentateuch but the Welsh translation by Richard Davies of some of S. Paul's epistles ; this latter manuscript found its way from Llannerch , the home of Gruffydd ap Ieuan and afterwards of his Davies (of Llannerch ) descendants, to Gwysaney, Flints. , the home of the Davies-Cooke family (q.v.) , also descendants. It is now at the National Library of Wales .

Gruffydd ap Ieuan was twice in. His first wife was Janet ( Sioned ) , daughter of Richard ap Howel of Mostyn ; by this marriage he was the father of Alice ‘ferch Gruffydd ap Ieuan,’ a poetess (q.v.) . It was by his second marriage, with Alice , daughter of John Owen of Llansantffraid , that he became the ancestor of the Griffith of Garn and Plasnewydd family . For some of the family connections see the articles in this dictionary on Davies (of Llannerch ) , and Davies-Cooke (of Gwysaney ) and Mostyn (family) of Mostyn ; see also lord Mostyn and T. Allen Glenn , History of the Family of Mostyn of Mostyn ( London , 1925 ).