The following is excerpted from a post to SGM, 10 Oct 1996, by John Yohalem:
Guy II inherited St. Pol from his niece, d. 1289, and by Mathilde of Brabant had three sons, most notably Hugh II of Blois and Guy III of St. Pol. Hugh's descendants, the counts of Blois, Soissons and Penthievre, included St. Charles and the Brittany claimants. This branch died out with Nicole, Ctss. of Penthievre, in 1479.