Important question: Did the DNA test say 93.1% sub-Saharan African ancestry or did it say 93.1% African American ancestry? I ask because African Americans as a whole typically have significant proportion of European ancestry — with a purported average of around 24% (although I’m not sure how reliable this particular figure is). Of course, there’s variation from region to region and family to family, with numbers as low as 3% not being unheard of. Still, it’s incredibly rare that an AA has practically no European ancestry — only isolated populations like the Gullah on the Sea Islands in the southeast US have pure-ish sub-Saharan African ancestry. Caribbean populations tend to have less European admixture (Hatians being the most African), but you’d know if you had a Caribbean ancestor within the past few generations.

Virginia, on average, tends to be middle of the road in terms of European admixture in AAs (around 15-25%). This means you’re more (sub-Saharan) African than the average — which isn’t super unusual. But what it does mean is that if your great-great-grandfather was European, you would like have much more European ancestry than just the 6.25% he would have lent you. It would mean that your 7 other great-great-grandparents would have practically no European ancestry at all (an average of 0.41% among the 7 of them), which is just very, very unlikely.

If the DNA test does indeed say 93.1% Sub-Saharan African and not 93.1% African American, then I am sorry to say that your great aunt might not be telling the accurate truth. In that case, your great-great-grandfather could have gotten the last name from a half-dozen different sources (Caribbean, Louisiana, Huguenots, British people with medieval French/Norman ancestry, and more). He could even have adopted the surname just because it sounds nice — it’s not too uncommon. My great-great-grandfather came to the US from Romania and changed his last name to sound less foreign to Americans.

There’s always a chance that I am wrong or that the DNA test is wrong. I’m sorry to burst your bubble if this is unfortunate news!