User blog comment:Crewlorinz/then who is ace.,,?/@comment-64.22.14.114-20090908050138

Ace is not genetically Luffy's brother. Ace is Gold D. Roger's son, and Luffy is Monkey D. Dragon's son. I'm pretty sure at this point Luffy does not know Monkey D. Dragon is his father(forgive me if i'm wrong). Luffy was raised by his grandfather Admiral Monkey D. Garp. When Luffy was about seven Ace was adopted into his family(for unknown reasons). So technically Ace is Luffy's adopted brother.