>>Apparently there was some precedent for the brother, in something unaired I believe.<<

I don't suppose you know what the unaired thing was. Because I'd far prefer it to be an interesting Gallifreyan definition of 'brother' like brother in arms or brother in school rather than the Master being the Doctor's biological brother, because that would be kind of dull. And totally ruin some of 3's stories, or at the very least make them make no sense, and I'm a 3 girl at heart so phooey to that.