Systyl ap DYFNWALL Lord of Upper Gwent
Shortly after the conference between the King and Welsh leaders, William de Broase invited Sitsyllt ap Dyfnwal, Geoffrey, his son, Jorwerth and many other cheftains(sic) of Gwent to a Banquet in the Castle of Abergavenny, and at a given signal slaughtered every man of them.
One account reads: 'Many nobles, including Sitsyllt ap Dyfnwal, were invited to the Castle under the pretence of peace and with the most solemn guarantee of safety. The real object of the gathering was to hear the laws of the realm, which forbade any traveller from carrying bow and arrow.