@Rin Btw Rin, I meant to talk to you.
So, old timey bigwigs have theorized that the Volsung Saga and Arthurian myth are very closely related, with details being borrowed and swapping back and forth. What with the Sword in the Tree vs the Sword in the stone, Sigmund becoming a legendary King and unifier like Arthur and a dozen other little details.
Anyway the parallels between Sinfjotli and Mordred are numerous. Both of them are bastards born of incest because their fathers witch sister changed her shape to sleep with him. Both of them killed their own brother/brothers, both had violent clashes with their father and both share their general status as the dark shadow to the main protag. It's fairly likely that Mordred and Sinfjotli are distant relations in terms of their legends roots, especially since the stories are supposed to take place very close to each other in time. They could be considered brothers from another saga if you will.
Anyway I was wondering if you were interested in trying to do anything with this, maybe have them find each other vaguely familiar in some way? Even if nothing else happens between the two I thought it would be cool to have this noted in some way, sort of like how Gilgamesh notes how Merodach and Caliburn are related, being from completely difrent legends, but also very similar in spirit.