Quote Originally Posted by theundeadhero View Post
I don't think GRRM would have made a point of talking about how the brotherhood used to be a part of the realm until one of the old Lord Commanders went in with the white walker lady and The North had to go in and take them out, which is why the brotherhood became a separate isolationist thing, without good reason. Although it is possible that old lord commander could be the mysterious white walker leader now reborn as one of them.
Potential spoilersThis has actually been more or less confirmed due to HBO accidentally naming the White Walker from S3E4 in their summary. It's him.