Is Christopher Tony's real blood nephew, or does he just call him that? To be Tony's nephew, he'd have to be the son of one of Tony's sisters, unless Tony has a brother or someone I've totally forgotten about. But watching the episode when Chris gets shot and his mother comes to visit him in the hospital, I had no idea who she was.
So in what way is Chris Tony's nephew?
This could be a really dumb question, but I just can't seem to figure it out.

My understanding is that Carmella is the cousin of the late 'Dickie' Moltisanti, a member of the Soprano/ Di Meo crime family who got killed.
Dickie Moltisanti was Chris' father. Dickie Moltisanti was Tony's mentor and introduced him to the way things were, when Tony's father 'Johnny Boy' wasn't available.

Dickie is Chris' father but died relatively young
and I think Chris can hardly remember him.
Tony feels that he is some way responsible for Chris and tries to perform the same mentor role that Dickie Moltisanti performed for him.

This partly explains the proximity and his reference to him as his nephew. I'm 90% sure of the above, but someone correct me please if I'm talking crap. I think the term Uncle is thrown around loosely. AJ refers once or twice to Uncle Silvio, Uncle Paulie and Uncle Jackie - though they are not blood relatives, just part of Tony's other family.

Hope this helps.

I have the same info on Chris Moltisanti's family background.

I just want to add that it's very common in Italian families to call cousins uncle and aunt if the person is very close and cherished. I guess it's because "Uncle Francesco" just sounds better than "Cousin Francesco".

And when you're a kid, every adult that's not your mother/father but often comes into your house, share meals and different activities, is called uncle/aunt.

And I didn't grow up in a crime family !!!

Most simply put, Christopher is the son of Carmela's cousin.

Here's a link to the Soprano family tree:

SOPRANO FAMILY TREE

So technically, Chris is Carmella's first cousin once removed.

Ah okay, I get it now. I call all my dad's friends Uncle too, but for some reason that didn't even occur to me.
Thanks everyone.