How to deal with a friendship my son (5yo) has struck up with the new kid

My son just turned five. He has always been shy, but late last year really started to come out of his shell, socially, at preschool. This is in large part to making friends with a great little kid. These two have been inseparable and I have loved seeing their friendship develop, and how they support each other and really care for each other. The teachers at school have all commented on how great it has been for both of them.Anyway at the start of this year a new boy has joined the class and my son loves him. Something about him always seemed kind of off to me, but what do I know - kids are weird. The energy between these two when they play is manic, and they often seem to point and shoot at other kids (which is discouraged by teachers), run around wildly, and never play with other kids at the same time, always just those two. I have noticed a drift between him and his best friend at school. When it's just the two of them at a play date they're fabulous, but at school the best friend is sometimes left on his own.We had a chance to hang out with a bunch of kids from preschool recently and it became clear that the new kid does not want other children playing with my son. All other kids are chased off. Additionally he is a real agitator. He tried to make one child steal a toy off another. He tried to force my son to slide down a slide when he didn't want to, which resulted in tears. He also initiated a game which my son joined in with that involved chasing best friend all over the playground and not inviting him to join the other games. He looked sad and my heart broke. I fear for my child's social development and empathy! but also for his friendship. I see a healthy friendship here being sidelined for an unhealthy one. I'm sure this is common, I remember having it done to me, but my parents didn't really handle anything.I don't like this new kid and I don't have faith that his parents will take my concerns here seriously. do I take this to the teacher? Do I talk to the parents? (Either of the new kid or the best friend). Do i talk to my kid? We have spoken to him about showing friendship and about how his behaviour may hurt his friends feelings and he may lose a friend. But I don't want to talk to him too much or in a way which overbears the point, if you know what I mean. Any advice appreciated, or perspective from people who've been here on either side. via /r/Parenting http://ift.tt/2nD3DwU