I think that just about every noble family in Western
Europe claims
Charlemagne (or Karl der
Grosse) among their many ancestors. Given the time that has passed and the limited size of the breeding pool (don't marry below your station), they are probably right whether or not it is the particular path they claim. Since there was a lot of "give the folks what they are paying for" research done by supposed genealogists, I am skeptical of any specific claim that that isn't backed up by more than one source.