 Upon the death of William , Lord of Glamorgan , his extensive holdings were eventually granted to Gilbert de Clare in 1217 . The subjugation of Glamorgan , begun by Fitzhamon , was finally completed by the powerful De Clare family , but although Gilbert de Clare had now become one of the great Marcher Lords the territory was far from settled . Hywel ap Maredudd , lord of <unk> captured his cousin Morgan ap Cadwallon and annexed Glynrhondda in an attempt to reunify the commotes under a single native ruler . This conflict was unresolved by the time of De Clare 's death and the area fell under Royal control . 
