Me and another girl like this guy. I found out he doesnt like her. How do i let him know i like him?

There is this guy i like and another girl likes him too. When talking to him, I found out the guy i like doesnt like the girl that likes him too. Since now i basically have him all to myself how do i tell him i like him without ruining our friendship? we have known each other since elementary school and aree good friends and i really like him. How do i start a conversation with him to tell him i like him?