How is it possible that i meet someone that looks like my brother?

Today I met a man that looks almost exactly like my younger brother. Is it possible to find someone that is not related to you that looks almost like you? He actually looks almost like my brother it freaked me out. The only differences i saw was that my younger brother is slightly more chubby, and the uber small details from their faces. How is this possible if that man my brother's twin. BTWs my brother is blood related to me, and all i know is we have only the two of us.