In the 10th Doctor episode [Smith and Jones](http://www.imdb.com/title/tt0974728/) when Martha asks the Doctor if he has a brother, he says

> 
> No, not any more. 
> 
> 
> 

It seems like if there had never been any mention of a brother, and no plans to introduce (a history of) one, a simple "no" would have worked for the purposes of this episode. 

Has there been mention of a brother in any other episode or any of the novels?