There's a whole theory and explanation. They are twins. It's been hinted at since the very beginning of the series. It's a very long theory but long story short, the twins were both kidnapped on the night of the mansion's fire. Our ciel (the protagonist to this story) witnessed his brother (the original ciel that was shown in this chapter) being stabbed. So our Ciel made a deal with the demon and assumed that the original ciel was killed. He took the name "Ciel Phantomhive" (with some evident hesitation as shown in the chapter of the flashback) in order to fulfil the duty of being the new earl. There's a better explanation on tumblr somewhere but I can't be bothered to look it up.
No no they don't have the same name, our ciel is actually not the real ciel, he just took his twin's name and lied about who he is. Or at least that's the theory going around
you could read more about the theory here
http://theofficialdoublecieltheorist.blogspot.com/?m=1
Ohhh is that so. Actually i didn't read this manga from the start. Since i watched its anime, I started reading from where it kind of left off.
Then I guess they are actually twins huh..
Oh well whatever it takes to make it more interesting is acceptable.
But thankfully Sebastian has one master. ٩(๑❛ᴗ❛๑)۶
Come on people, whats wrong with u all. Why are u considering an imposter to be Ciel's twin?
Even if he were his twin, don't u think that he would have a different name.
Or do you think that twins have same name?
LOL..(〜￣△￣)〜