Ieuan ap Gruffydd of Llanuwchllyn and Cevn Trevlaith
- Marriage (1): Gwenllian verch Ieuan ap Howel
- Marriage (2): Annesta verch Llewelyn ap Einion
- Died: 1370
- Buried: Llanuwchllyn, Llanstundwy, Evionydd, Wales
From History of the Princes, the Lords Marcher, and the Ancient Nobility of Powys Fadog, p. 121:
"Ieuan ab Gruffydd, of Llanuwchllyn and Cevn Trevlaith, in the parish of Llanstundwy in Evionydd. He died in 1370, and was buried at Llanuwchllyn, where his tomb still remains, on which he is represented in armour, with a shield charged with the arms of his house, and this inscription, 'HIC IACET IOANNES AB GRIFFIT AB MADOG AB IERVERTH, CVIVS ANIMĘ PROPITIETVR DEVS. AMEN. ANO. DNI. MCCCLXX.' He married, first, Gwenllian, daughter and heiress of Ieuan ab Howel ab Meredydd ab Einion ab Gwgan ab Merwydd ab Collwyn ab Tanguo, Lord of Evionydd and Ardudwy, one of the Noble Tribes, who bore, sable, a chev. inter three fleurs-de-lys argent, and who lived for some time at Bronwen's Tower in Harlech, whence it was called Caer Collwyn. By this lady he had issue a son named Owain, who succeeded to Cevn Trevlaith. Ieuan married, secondly, Annesta, daughter of Llewelyn ab Einion ab Meilir Grūg, Lord of Trev Gynon (sable, a chev. inter three horse's heads erased argent), by whom he had a younger son, Rhys of Cyn Llwyd, of whom hereafter, and an elder son-- Ieuan Vychan of Llanuwchllyn..."
Ieuan married Gwenllian verch Ieuan ap Howel.
Ieuan next married Annesta verch Llewelyn ap Einion, daughter of Llewelyn ap Einion ap Meilir Grūg Lord of Trev Gynon and Unknown.