When Sirius tells of his brother Regulus dying he says that he wanted to leave the Death Eaters and was killed, however it is likely that he knew he would be killed upon leaving and faked his own death. My evidence of this is the article in the Quibbler, which stated that a woman had seen 'Sirius Black' under the guise of Stubby Boardman, a year after Regulus's death, and had dinner with him. It is possible that Sirius' brother looked like him and was laying low to avoid the Death Eaters.

I never would of thought of that! Wow... Ummm. Yah that sounds really good! Because if he was younger he would have a 50/50 chance of looking like Sirius.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Difference between genius and stuppidity is that genius has it's limits.
I'm on the lower end of the scale.

It's a really good theroy, but in a chat in March or somthing like that, J.K confirmed he was dead.

"Wouldn't expecting the unexpected make the unexpected expected?"

Did she say that Sirius was dead or that his brother was? His brother might perhaps appear in a future book?

Yeah, someone actually asked about Regulus being really dead? Odd.
But JKR also has a tendency to forget what she says in interviews, so there's always a chance.
I think Regulus would be a highly interesting character to add to the stories. There's a lot of depth to go off there- a man who was of the true Black line, believing in the Black ideals, but then turned from them. I think most people would figure he left as a coward, unable to complete Voldemort's demands, but there might have been more there. I wish JKR would say something more on it.

I found the transcirpt:

* Cathedral: Will we be hearing anything from Sirius Black's brother, Regulus, in future books?
JK Rowling replies -> Well, he's dead, so he's pretty quiet these days.

"Wouldn't expecting the unexpected make the unexpected expected?"

Hence the phrase "PRETTY QUEIT these days".

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Difference between genius and stuppidity is that genius has it's limits.
I'm on the lower end of the scale.