On Radio 1 the other day, one of the presenters came up withan idea and asked DT if CJ was the Doctors brother?
DT's reply was you will need to wait and see..

Obviously it is still a mystery as to who he is. Would be a great twist if it turns out to be correct...

Didn't the doctor explicitly say he's a human from the 51st century in (new) season 1?

hmm i doubt he is the Doctors brother, we would deffinatly know by now. im quite curious how the dr becomes a human in this series and what he is gonna do about martha?? after seing the new trailer she seems to be in trouble and he says im not the doctor.... what spurs him to become the doctor again???

I doubt there would have been the homo-erotic frisson between them (I'm thinking Eccleston here) were they brothers...

Does CJ really know who he is as there is till the memory loss and missing two years to explain.

He's only missing two years. Surely he knows who he is - just not what he was doing for that two year period.

depends on what was wiped from his memory. surely it is possible they could have given him a new identity?

It's possible, I guess .... But then again, that's possible of any character without much more of a leap of faith.

was just a thought as they have went to great lengths in Torchwood to retain the mystery of the character.

Why not go the whole hog and reveal him to be the Doctor's son as mentioned last series. It's probably been mentioned already.