As of yet we have absolutely no idea. Alot of things point to them being related somehow such as appearance and the D. but also (SPOILER!!!!! HUGE SPOILER!!!! Don't read if your not fully caught up on One Piece!) Ace and Luffy are not related and Ace is the son of Gol D. Roger. I'm pretty sure Luffy isn't at least closesly related to Roger because Ace's mother died while giving birth and Roger had already been executed so Luffy being Roger's son is deffinately a no. Or at least most very likely a no. Again nothing has been said.
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no it his uncleluffys dad is monkey d. dragon. he might be his uncle.Strong points that they may be related:Ace was adopted by the "monkey family" (luffy,dragon,garp)Ace is Gol D. Roger son, (not Gold Roger or Gold D. Roger)"Will of D"
yes but he has to absorb about 100 shadows to become nightmare Luffy
Hancock and luffy's crew and shanks
Goku wins by blowing up the planet luffy is standing on.
No, the dark lord (raylegiah) allreadt taught luffy that.