The numbers have even changed. It's is now 1 out of 150 kids born with a form of Autism. I bet he knows someone else who has it and hasn't realized it yet.
My son is seven, he has PDD-NOS, which like aspergers is on the autism spectrum. He doesn't know he has a "diagnosis". He feels good about himself now, suspects nothing different about him, so we are waiting until he starts to have questions. I feel so bad how your brother found out. It was very inappropiate of the teaching staff to let that happen, but it did and you are going to have to really help him during this time. Family is the most important thing in anyone's life and he is very lucky to have a sister like you.
What I'm planning on saying to my son when we get to that point is "your brain is wired different, not better, not worst, just different." I think it is a hard thing to handle what ever age you are ......especially 14, but if he has a big sister who loves him and says he is ok, he will feel it. Try to give him the confidence that he is struggling with now. Point out all his strengths and I bet he has so many of them!!!!!
I have also heard of a book, "Freaks, Greeks and Asperger Syndrome," by Luke Jackson. It's about a 13 year old describing his aspergers. Try looking in your local library. I bet you'll find it and it may really help him. Especially their age being so close.
Good luck, I hope some of this was helpful. This site is really useful. It not only has parents, siblings, friends, teachers, but kids and adults with aspergers. Keep it in mind in the future