I did some searching and found out that he was like 80% a direct descendant to Charlemagne, so did he have some sort of legal claim to becoming the king of France?
This old answer by /u/Georgy_K_Zhukov details why pretty much everyone of European descent will have X famous European historical figure as an ancestor, even using the specific example of Charlemagne!
https://www.reddit.com/r/AskHistorians/comments/20pubn/comment/cg5u0wo