Rambam, Hilchot Milah 1:7 says that a convert must be circumcised before his conversion is complete. If he was already circumcised when he was not Jewish, a Hatafat Dam Brit (taking a drop of blood) must be done.
What if the convert received a halachically valid circumcision when he was 8 days old, does he have to do Hatafat Dam when he converts? For example, his mother thought she was Jewish, and didn't find out until after her son was circumcised that she was in fact not Jewish. When the son was 8 days old he received a proper, halachic circumcision. Does that circumcision count for the conversion process?
In other words, do we say that the reason the already circumcised convert must get Hatafat Dam Brit is because the first circumcision wasn't a halachic one? (In which case the convert in question did receive a halachically valid circumcision)
Or do we say that the reason he must get Hatafat Dam Brit is because the previous circumcision wasn't done with the intention of converting? (and therefore it doesn't matter whether the previous circumcision was halachically valid or not, it was not done as part of the conversion process)
Note that I am not asking about Giur L'Chumrah. I am asking if the son is doing a complete conversion (e.g. after the mother found out she wasn't Jewish she elected not to convert. The son decided to convert later on in life, and goes through a complete conversion process)
Additional Note: Rambam, Hilchot Issurei Biah 13:1 says that the Jewish People also did the three steps of conversion before the Torah was given. The circumcision was done in Egypt, before the Jews ate the Korban Pesach. It could perhaps be argued that they did not know they were circumcising themselves as part of the conversion process. If so, perhaps a parallel could be made to our case, where the original circumcision was not done with the intent to convert, but it was still halachically valid for the conversion process. (Also, the tribe of Levi never stopped circumcising their children, so they definitely didn't have in mind the conversion process)
Someone just told me that this question was discussed in connection to the Ethiopian Jews, and is discussed in Ovadia Yosef's Yabia Omer and other places. I haven't looked any of them up yet.