The humiliation does not rest in the fact that the Queen was assumed to be Black, the humiliation comes in a society that determined that Black and Queen could not inhabit the same body. That a black body was not even worthy of entering the front door.
I never knew this and found it very interesting. I also liked how it pointed out systematic racism not just in individual actions, but in structures that define worth and dignity. The issue isn't the idea of a Black Queen, but that society couldn’t even imagine it as possible or acceptable.