Oman gives these notes concerning a possible marriage of Hywel:
(Research):MARRIAGE: Investigate> Dwnn's 'Heraldic Visitations of Wales' volume 1 page 297 gives as his wife Annes "Goch" ferch Ieuan ap Moelwyn to Ethelystan.
MARRIAGE: Investigate> Lloyd's 'History of the Princes, the Lords Marcher and the Ancient Nobility of Powys Fadog' volume 5 page 114 gives his wife as Annes "Goch" ferch Ieuan ap Y Moelwyn, Lord of Buellt.
CONCLUSION: Because of the generational time frame separating Hywel and this Annes it is highly improbable that she was his wife.