Sadly, that's common. I'd probably keep him until he started crowing, while formulating a plan on how to deal with him once that happened; rehoming him or processing him for the freezer. I've not had Brahmas, so do not know if they go broody, or if you have an incubator, but if you were so inclined to hang onto him as long as you could... you might get some chicks from him that you could raise up to fill out your flock with hens... and of course... rehome or repurpose the boys from that hatch.