In the Lancelot-Grail Merlin, Igraine is provided with two earlier husbands, one named Hoel who is the father of two daughters: Gawain's mother and a daughter named Blasine who marries King Nentres of Garlot.
It is possible this Hoel derives from Geoffrey's confused statement that Igraine's eldest daughter had by her first husband Howel which was misunderstood to refer instead to a supposed first husband of Igraine named Howel/Hoel.