De Forz
Mabel Malet's and Hugh de Vivonia's son is referred to as William de Forz (de Vivonia). During the same time frame, there were three generations of Earls with the name of William de Forz. Both William Malet and William de Fortibus (Forz) are on the Magna Carta list. Some have suggested a relationship between the families.
Read more about this topic: William Malet (Magna Carta)