First I call Weevil the illegitimate child of Whitebeard because I am 100% sure he is not Whitebeard’s son.
Whitebeard obviously has much more morals than Bakkin, so there is no way he actually fell in love for her. It is 100% true she hooked up with one hell of a fighter though.
The illegitimate child’s character design and unique characteristics are key. Further anti-Whitebeard context is that he talks like a country-bumkin. Although Whitebeard uses stereotypical “tough-guy” talk, he is actually very refined in how he talks (think of the flashback on Whitebeard saying his dream is to “have a family” and everyone laughs at him). With how excessively physical and personality traits are carried through genetics in the One Piece world, the country accent is from his true father.
This is biased towards Japanese readers, but he constantly talks like he has a runny nose (he regularly has to sniff up the stuff too). I’m thinking the twist is that Bakkin constantly has to reinforce the glue to hold the fake Whitebeard mustache, so the strong glue is why he has to talk the way he does.
Now for the meat of the theory: we know Bakkin wants to go after Luffy. So the illegitimate child of Whitebeard will meet Luffy and probably relatively soon.
The biggest key is that they both HATE Blackbeard. Luffy’s got more than enough reasons, but Weevil is a pure and naive idiot so he truly believes Blackbeard killed his father.
He will listen to his mother’s orders initially (to go after Luffy), but the topic of Blackbeard will come up (and Blackbeard making a move might be the trigger). In typical Luffy fashion, he wins Weevil over and Luffy forces Bakkin’s true nature to come out. Seeing Bakkin’s manipulative ways, Weevil makes the choice to choose Luffy over Bakkin.
Weevil immediately becomes the strongest underling in the Grand Fleet.
*Theory by Seiryu