Actually, Tim Armstrong is not Billie Joe's brother, nor are they cousins, even though they have the same last name. However, Tim and BJ do get along. FYI, Tim was in Operation Ivy (he went by the name Lint), the band that wrote Knowledge which Green Day covered and plays at many of their concerts. Billie also helped Tim write the song "Radio" on Rancid's "Let's GO!" album.