Prior to the arrival of the Normans, Twthill was a court of the kings of Gwynedd. What we see today, however, are the remains of a ‘motte and bailey’ castle erected by Robert of Rhuddlan in 1073. A kinsman of Hugh d’Avranches, the Earl of Chester, Robert attempted to consolidate Norman advances in north Wales after the conquest of William the Conquerer. Twthill was Robert’s base, and from it he subdued much of Gwynedd until his death in 1193.

The area around Rhuddlan Castle was reunited with Gwynedd as part of the campaign of Owain’s father, Gruffydd, that cost the life of Owain’s elder brother, Cadwallon in 1132. Cadwallon killed some of his own uncles in order to achieve this. Owain’s marriage to Cristina reconciled these two sides of the family. The campaigns of 1136/37, which brought Ceredigion into the fold, expanded Gruffydd’s (and then Owain’s) hold over Wales to include all of north Wales and most of the west coast.

Earlier, Robert of Rhuddlan controlled both Deganwy and Rhuddlan (these locations are referred to as in the hands of the Earl of Chester in the Wiki quote below), but Gruffydd killed Robert in 1093 and I find no indication (other than the quote below) that Normans regained control of either site after his death. (For example, a quote here: “Robert’s lands in Gwynedd were now taken over by Earl Hugh of Chester, but the Welsh revolt of 1094 led by Gruffydd ap Cynan resulted in the loss of most of this territory.” http://en.wikipedia.org/wiki/Robert_of_Rhuddlan)

I draw your attention to this map: https://sarahwoodbury.com/wp-content/uploads/2010/11/565px-Cantrefi_Medieval_Wales.jpg
along with some further wikipedia information. The cantrefs in question are Rhos, Rhufoniog, and Tegeingel, all of which intersect at Rhuddlan.

“In 1120 a minor border war between Llywarch ab Owain, lord of a commote in the Dyffryn Clwyd cantref, and Hywel ab Ithel, lord of Rhufoniog and Rhos brought Powys and Chester into conflict in the Perfeddwlad. Powys brought a force of 400 warriors to the aid of its ally Rhufoniog, while Chester sent Norman knights from Rhuddlan to the aid of Dyffryn Clwyd. The bloody Battle of Maes Maen Cymro, fought a mile to the north-west of Ruthin, ended with Lywarch ab Owain slain and the defeat of Dyffryn Clwyd. However, It was a pyrrhic victory as the battle left Hywel ab Ithel mortally wounded. The last of his line, when Hywel ab Ithel died six weeks later he left Rhufoniog and Rhos bereft.  Powys, however, was not strong enough to garrison Rhufoniog and Rhos, nor was Chester able to exert influence inland from its coastal holdings of Rhuddlan and Degannwy.  With Rhufoniog and Rhos abandoned, Gruffydd I annexed the cantrefs.[23]

On the death of Einion ap Cadwgan, lord of Meirionydd, a quarrel engulfed his kinsmen on who should succeed him. Meirionydd was then a vassal cantref of Powys, and the family there a cadet of the Mathrafal house of Powys. Gruffydd gave license to his sons Cadwallon and Owain to press the opportunity the dynastic strife in Meirionydd presented.  The brothers raided Meirionydd with the Lord of Powys as important there as he was in the Perfeddwlad. However it would not be until 1136 that the cantref was firmly within Gwynedd’s control. Perhaps because of their support of Earl Hugh of Chester, Gwynedd’s rival, in 1124 Cadwallon slew the three rulers of Dyffryn Clwyd, his maternal uncles, bringing the cantref firmly under Gwynedd’s vassalage that year.[23] And in 1125 Cadwallon slew the grandsons of Edwin ap Goronwy of Tegeingl, leaving Tegeingl bereft of lordship.” http://en.wikipedia.org/wiki/Kingdom_of_Gwynedd#cite_note-Tegeingl-21

It was at the old castle of Twthill that Llywelyn ap Gruffydd made his obesience to King Edward of England after the 1277 war, after which he pulled it down and built the massive stone Rhuddlan Castle that stands today.