Ellie Rowsell said this quote

“ I’m not really one to write simplistic and jovial lyrics, and while on the surface I can see how “Bros” is a happy song – a celebration of friendship and one’s younger years – I see a panic in the words. Particularly the bridge, which I think expresses the fear I had, not of growing up, but of growing up without Sadie. I don’t know which one of us started having trouble entering the Fourth World first – I’d like to think it was me because I was a year older, but I don’t think our age difference was mirrored in our maturity. Either way, I worried that once we entered reality as budding adults – no longer pretending to be “raised by wolves and other beasts” – we wouldn’t be together all the time. ”