User blog comment:PirateKnight19/Luffy's Father sailed with Gol D. Roger/@comment-25400375-20170528203807/@comment-174.119.202.204-20170528232115

Like I said it's just a thoery. As for joining Roger ran into Rayleigh and called it destiny and Crocus they met once they entered the grand line and he tagged along cause of Roger's health.