Extract from FB post by Scott Parkey (Excellent work)
This may be the only reliable pedigree from the time to trace back to these kings. That means that to prove that you descend from the Kings of Cornwall, you must prove descent from Morgan Hen.
Can anybody do that? Well, many Welsh aristocratic families kept good pedigrees, highlighting their ties to powerful ancestors. The more powerful, the better the descendancy was kept. After the Norman Conquest, Morgan Hen's descendants still held some power, but nothing compared to, say, the descendants of his father-in-law Rhodri Mawr. So a few families claimed descent, but not an overwhelming amount.
Did any end up back in Cornwall? I've had trouble pinpointing these Welsh families in the Cornish pedigrees, so although there are likely multiple, I've only found one so far: Sybilla Morgan m. Hugh Trevanion of Caerhays Castle.
Sybilla has quite the descendancy that even includes Windsors. But there are also some regular Cornish folk in there. So it does seem that after all, the known (or as known as we can get for such long times) descendants of the Kings of Cornwall have returned
