Sorry Isaac, I'm not a great Latin scholar, but I am curious as to why you think Alice de Montfort, the widow of Gilbert de Gant or Gaunt would have married Henry de Essex?
I've learned never to say something is impossible in medieval genealogy, but chronologically they look to be in totally different generations.
I'm citing Keats-Rohan and admittedly haven't checked her sources, but she has Gilbert de Gant the husband of Alice de Montfort (who she names as Gislebert de Gand) as died circa 1095 (Domesday People, p. 210) and Gilbert's son and heir Walter de Gant/Gand as died in 1139 (Domesday Descendants, p. 472) and Walter's son, Gilbert II, Earl of Lincoln as died in 1156.(DD, p. 471).
Yet Henry de Essex, succeeded his father by 1146 and died sometime after 1163 when he was defeated in battle. (DD pp. 449-450). So given life expectancy in this period, it seems highly likely that he wasn't even born when Alice de Montfort became a widow in circa 1095, and is probably of the generation of her grandson?
Unless you mean a different Henry of Essex or Alice de Montfort?
Like any source Keats Rohan's books can have incorrect information, and there are some corrections to the entries for Henry de Essex and Walter de Gand (look for the page numbers I have cited) but not concerning the marriage of Alice de Montfort.