How Can I Tell My Brother

I have been atheist for a while now. If I told my parents they would go bat shit insane to where I couldn't even think of what would happen. However, My brother, while he is christian, he believes heavily in science and evolution. I have always been able to tell my brother anything, but I don't know how to tell him this. Please I need help, not telling anyone is killing me and I have to tell him first.