He isn't a secret, but he isn't known either.
Edit: Please also check out Supersiblings.org for more insight into the family dynamic.
Update 4/2/2015: Removed some ableist language and links to a problematic info source. I would also like to note that despite the differentiation I argue between "retarded" and "stupid," words that insult intelligence can also be ableist and often classist. Think of why you use them if ever.
For reasons that should be clear, I did not write my brother's name in this blog. This is to protect him and the residents of his group home.