In Your Shadow, page 7.

There wasn't anyone on the school grounds that Sirius didn't know, and after James, he was the most famous...
Compared to the other two, Remus was reserved, but he had a nice personality and was popular. He was nice even to me...he was kind-hearted.
My happiness only lasted for the first one or two years.

Snape: Hey, Peter.

He was a Slytherin named Snape. He hated everything about James with a passion (and James too, but..).

Peter: Wh-what?