For all or most of his childhood, a usurping cousin ruled in Budic's place and the family resided in exile with Aergol Lawhir, king of Dyfed in sub-Roman Britain.

He died shortly before he would have inherited the throne, however,[1] and Budic's attempts to enlist his neighbour Macliau's support for the succession of Hywel's son Tewdwr ended badly.

A conflation of the two appears prominently in Geoffrey of Monmouth's pseudohistorical Historia Regum Britanniae, where Hywel comes from Brittany to help suppress the revolts which arise after Arthur's coronation.

In Geoffrey, Hywel's niece is raped and killed by the Giant of Mont Saint-Michel; Arthur sets off to slay him with Sir Kay and Bedivere.

In these stories, Hywel is duke of Brittany and the father of Tristan's unloved wife, Iseult of the White Hands (Iseut aux Blanches Mains).

In early versions of the story, Tristan remains in Hywel's land until he dies of poison minutes before Iseult of Ireland, a great healer, arrives to cure him.

[6] The present parish church at Llanhowell (Welsh: Eglwys Llanhywel) was largely refurbished in the 1890s but includes sections dating as early as the 12th century.