A difficult question, because it is very incredible to imagine that Garp would have a very close relationship with someone (well, you get the idea), but the very fact of the existence of the Dragon refutes the option of division (like in cells). So, options for moms… Bogart, yes, (I'm writing all this for fun, relax… or not?))). So, the evidence is based on the fact that Oda draws Garp with a straight nose, and Dragon with a hump, and this is confirmed in the manga (checked several times, since it was a manga and nothing would stop me from thinking that way, why not? WE LITERALLY HAVE THERE IS A CROCO-MOM THEORY. Why can't we have a Bogarde-mother? Maybe it's a family thing). Who else in Garp's circle has a hooked nose? With Bogart, everything, everything fits. Dragon always has a dark and displeased face, like Bogart. Another candidate is Tsuru and Sengoku, but what tells me is that they themselves kicked Garp to hell, and Sengoku actually got married at work and has no time for that🙃 Although the presence of Tsuru’s granddaughter refutes this topic and perhaps she got along with Sengoku. And no one except Bogart is apparently ready to tolerate this asshole (Garp) getting into trouble.