During the latter part of the twelfth and early thirteenth centuries, the castle was again the scene of many conflicts, this time during the wars between the Welsh and the English. Indeed Rhys Gryg, the son of the Lord Rhys who fought for the English cause, was forced to dismantle the Castle by Llywelyn the Great, Prince of Gwynedd, who was pre-eminent in the area during the early part of the thirteenth century.
In the later
part of the 13th century the English crown had to respond to the threat
of the increasing power of Llywelyn ap Gruffudd 'Llywelyn the Last' of Gwynedd. When an English force met a Welsh one on a battlefield at Coed Llanthen near Llandelio, the ensuing battle resulted in a resounding English defeat. The castle at the time was in the hands of another son of Lord Rhys, Rhys Fychan, an alley of Llywelyn the Last.
When the death of Henry III occurred in 1272, Edward I came to the English throne. Within five years he had destroyed the power of the Welsh princes, In 1276 an English army under Pain de Chaworth was assembled at
Carmarthen, and as it advanced up the Tywi valley Welsh resistance crumbled. Rhys Wedrod, at the time in control of Dinefwr placed the castle
in the king's hands after which the castle remained largely in possession
of the English crown.
After the castle was succeeded to the English crown, an English castellan was put in charge after which expenditure accounts inform us that repair work was undertaken
ditches were cleaned out, the tower, bridge,
hall and the "little tower' were repaired, a new gate was built
and five buildings were erected within the outer ward. Further repairs
were carried out in 1326. But as time past and tensions eased the English garrison moved out and the castle was left to fall into disrepair.