About Owain Eurgen ap Marius Cyllin, King of Wales
See Darrell Wolcott, http://www.ancientwalesstudies.org/id145.html, for untangling of these lines. (March 18, 22017, Anne Brannen, curator)
Eurgen and Gladys are not known to occur in any source earlier than a chart (with no soures cited) in R.W. Morgan's "St. Paul in Britain: or, the origin of British as opposed to Papal Christianity" (19th cent.!). Wurts often quotes Morgan verbatim. That is why no one knows who Eurgen's husband was (the name is feminine, though I doubt either realized it). The bit about Lucius and Coel is drawn from the Iolo Manuscripts (18th cent.), which is probably based upon, though ostensibly distinguished from, the Lucius son of Coel in Geoffrey's HRB.
The earlier form of the Lucius legend, which omits his father, was known to Bede (8th cent.), but from what he tells us it is all probably based on misidentifying Lucius of *Britium* on the continent as a British king.
FROM BRITANIA.com: Legendary Kings of the Silures According to the Brenhinllwyth Morganwc