Responses
I don't think so because if it were Vince than Undertaker wouldn't be so sad at his death. He would know if he is still alive and If Ciel had a twin we would know by know. I think he is probly related some how.
My theory is that the guy use his "water" in the tea to define what type of blood does a person has and it's look like Ciel had the type AB because the guy say it's rare and AB can be given to anyone, so this guy "Sirius" is receiving blood from everyone that is compatible to his like Violet.
Is there any chance of that new boss of the starish, Sirius, being Ciel's father?
Since they probably have the same type of blood right?
Or maybe... Ciel's twin?