Comment by teruakohatu

The Kingdom of Kongo had a civil war resulting two factions claiming the throne and a lot of victims being enslaved and being sent to South America. The monarchy was only disestablished in 1914. The ancestral story mentioned in the article is quite plausible.

https://en.m.wikipedia.org/wiki/Kongo_Civil_War

I am not sure where Uganda comes in, possibly the king has other relatives from there.