This cut has been caused by a sharp implement. This may also be a post-mortem ‘punishment’ blow as the torso would have been protected during battle by a solid backplate.
This was produced by a sharp weapon from behind. The angle of the blow suggests that this was caused by a weapon being thrust into the right buttock. Such a blow would be difficult to inflict during battle, when the King would have been protected by armour. This might suggest that this injury was also caused post mortem, as an act of humiliation.