Comment by Ace Bng on One Piece - Chapter 1121

@Ace Bng well from what I've heard it's shanks brother.

@Sarah where did u hear that from?

@Ace Bng isn't that shanks dad or w.e

@AJ NAIR I wonder too🤔

@Emyln Ashe Isn't Garling Figarland (the moon shaped head guy) supposed to be Shanks' father?

@Ace Bng garling being Shanks' father is just a fan-made theory. A theory I have heard now is that, the silhouette shown under dragon is His evil twin(and he's the one who was talking to gorosei during wano arc).

@AJ NAIR Like 99% of One Piece theories it's just a wild guess so until Oda sensei says otherwise Shanks doesn't have a brother.
For Garling just like you said he is supposed to be Shanks' father so it's just an hypothese that comes from OP Red movie