I have serious doubts about this William de Bologne as a son of Eustace II of Boulogne. I find no record of him anywhere other than as the son of King Stephen of England or the grandson (through Geoffrey FitzEustace) of Eustace II. I think the later is the most likely. But, even then, I have found no definite connection to a son named Tristan. What is the source of your information?
