I'm slooooowly doing a rewatch of NuWho, and I'm up to "Smith and Jones". At the start of the episode, when Martha is examining 'John Smith' in the hospital, after earlier running into Ten on the street, she asks him "have you got a brother?", to which he replies "no, not anymore, just me".

Keep in mind, at this point The Doctor thinks he's wiped out all of Gallifrey, including his own family, and that he's the last Time Lord.

I suppose you could consider it flowery language, and he's referring to The Master, or simply that he's lying as part of his John Smith persona, but it feels like a deliberately loaded line to continue establishing The Doctor's complete loneliness.

So this got me wondering - we know of his granddaughter Susan and his presumable child(/ren) before her, but has a brother for The Doctor ever been established before, even if just in expanded universe media such as books, comics, or audio?