Guy DE MONTFORT Seigneur de Ferté-Alais et de Castres-en-Albigeois
- Married (2): Bef Jul 1224
- Died: 31 Jan 1228-1229, Battle of Vareilles, Ariege, Foix, France
- Buried: Abbaye de Haute-Bruyère, Saint-Rémy-l'Honoré, Yvelines, Île-de-France, France
The Chronicle of Alberic de Trois-Fontaines refers to the mother of "comes Symon Montisfortis et Guido frater eius" as "Guilelmum comitem Licestrie…sorore". The Lignages d'Outremer name "Gui de Monfort" as brother of "Symon le conte de Montfort". A charter dated Feb 1199 recalls a donation to the leprosery of Grand-Beaulieu near Chartres by "Amauricus de Monteforti", with the consent of "Amauricus parvus filius eiusdem Amaurici, qui erat sub custodia Amaurici de Mestenon", and the confirmation by "Simon de Monteforti, predictorum successor virorum et heres" with the consent of "uxore mea Eva [presumably an error for Alix] et filiis meis Amaurico et Guidone et fratre meo Guidone". "Symon dominus Montisfortis et Guido frater meus" confirmed donations to Saint-Martin-des-Champs made by "comes Amauricus abavus noster" by charter dated 1 Jan/9 Apr 1200 or 1 Jan/25 Mar 1201.
Seigneur de Brétencourt 1202. "Li cuens Symon de Monfort et Gui ses freres" left on crusade in 1202. Villehardouin records that, after the siege of Zara, "Simon de Montfort [and]…his brother Guy de Montfort" deserted the army to join the king of Hungary.
Seigneur de Ferté-Alais. The Continuator of William of Tyre records that, after their arrival in Palestine, "li cuens Symon de Montfort" remained in the land and "ses freres Guis si prist a feme la dame de Saete". The Chronicle of Ernoul records the arrival of "li quens Simons de Montfort, et Guis ses freres" in Palestine [in 1204] and that "Guis prist à feme le dame de Saiete".
Seigneur de Castres-en-Albigeois: the Historia Albigensium of Pierre de Vaux-Cernay records the return "a partibus transmarinis" of "comes…Guido frater eius germanus" who held "castrum in diocese Albigensi…Castra", dated to  from the context. "Guido de Monteforti" donated property to "ecclesiæ de Pruliano", with the consent of "uxoris Alicis Sidoniæ dominæ", by charter dated 1 Jun 1216.
The necrology of Haute-Bruyère lists members of the Montfort family who are buried in the abbey, including "…conte Gui de Sagette qui fut frere du conte Simon…"
Guy married Helvis IBELIN of Nablus, daughter of Balian III D' IBELIN of Ramla, Lord of Nablus and Maria KOMNENE of Byzantium, Lady of Nauplia. (Helvis IBELIN of Nablus was born about 1182 and died before 1 Jun 1216.)
Guy also married Briende DE BEYNES, daughter of Baron Lambert Adémar DE LA GARDE co-Seigneur de Monteil and Tiburge DE BAUX, before Jul 1224. (Briende DE BEYNES died on an unknown date.)