That's something that always made me wonder, and since I'm currently writing a story set in a feudal world (I know, original /s), I thought I might as well ask: How far in the line of succession do you need to be to no longer be considered a noble? I mean, logic, as far as I'm concerned, will mean that eventually, *everyone* will have a royal/noble ancestor. How did they deal with this problem? Was there a specific cut-off point, or hell, even a law that said something along the line of: "If you're the third son of the third son of the king's cousin, you can't claim the family name of the Valois at all"?
Hi there - we're happy to approve your question related to your creative project, and we are happy for people to answer. However, we should warn you that many flairs have become reluctant to answer questions for aspiring novelists and the like, based on past experience: some people working on creative projects have a tendency to try to pump historians for trivia while ignoring the bigger points they were making, while others have a tendency to argue with historians when the historical reality does not line up with what's needed for a particular scene or characterization. Please respect the answers of people who have generously given you their time, even if it's not always what you want to hear.
Additionally, as amazing as our flair panel is, we should also point out that /r/AskHistorians is not a professional historical consultation service. If you're asking a question here because you need vital research for a future commercial product such as a historical novel, you may be better off engaging a historical consultant at a fair hourly rate to answer these questions for you. We don't know what the going rate for consultancy work would be in your locality, but it may be worth looking into that if you have in-depth or highly plot-reliant questions for this project. Some /r/AskHistorians flairs could be receptive to working as a consultant in this way. However, if you wish for a flair here to do this work for you, you will need to organize this with them yourselves.
For more general advice about doing research to inform a creative project, please check out our Monday Methods post on the subject.