Ieuan ab Owain Glyndŵr was reputedly the illegitimate son of Owain Glyndŵr, the last native-Welsh Prince of Wales. The possibility of his existence was uncovered through the work of Peter Bartrum which is currently being edited by the University of Wales Aberystwyth. Ieuan ab Owain and his descendants are detailed in Peniarth Manuscript 287 in the hand of Robert Vaughan of Hengwrt (c.1592-1667) and also in the manuscript known as Harley 1969 by Griffith Hughes (1634–1665) - the original manuscripts are kept at the National Library of Wales, Aberystwyth and the British Library respectively.
Ieuan, who is thought to have been born around 1380 and to have died around 1430, is thought to have had three sons:
. J. Gwenogvryn Evans . Report on Manuscripts in the Welsh Language. 1st . volume I . Historical Manuscripts Commission . London. 1898 . Report on Manuscripts in the Welsh Language. . 2008-06-01 .