For anyone who played Uncharted 3, *spoiler alert* it was revealed Drake was not actually a descendant of Francis Drake but an orphan whose parents were killed. I believe this long lost brother will turn out to be a long time friend Drake double crossed some time before U1. I think that voice over from the original reveal (the actor left the project) is the character Troy Baker is now playing. Nolan North and Troy Baker are brothers (in law) in real life and TLOU behind the scenes reveal they love working with each other. Their chemistry should rival Nate and Sully's. This characters introduction also makes me believe Sully will definitely be the one who dies in the game. Future games (oh there will be more fans) will revolve around these two. 

Drake dies and this new character becomes the protagonist in future, spiritual sequels.

Nice theory.

"Liquid drake" kind of looked like an older,balder drake though...

Cool I didn't know North and Baker were bro's in law. Game wise it could be either. Siblings can be orphans together you know, and they can have quite the falling out, like Joel and Tommy in TLOU and not see or talk to each other in years.

Drake is king! No need for sequels if he dies.

Reasonable assumption

I personally never thought they were blood brothers, but I'm sure Naughty Dog will make a good story. In Naughty Dog I trust

More stinky spoilage below!

Yeah. It's good to introduce someone new before taking the old one way, but a thief's end could refer to any character in the game. Once upon a time, in Uncharted 3, wasn't some people expecting Sully to suddenly turn into the bad guy, or get killed?

It never happened.

kinda reminds me of flynn. oh by the way naughty dog: can we have storyline-coop this time?

I think they will be actual brothers. You could be right about Sully. I think this will be the last uncharted for a while but they will leave it open to a sequel either way as uncharted is a very important IP. Though it is important for Sony to kelp building strong IP and naughty dog will be encouraged to create brand new stuff for their next few games.

No one thought the possibility of him being Sully son?