Just saw a theory online that blew my mind.
Brook is Aokiji's grandfather.
- They genuinely have the same appearance. Even same faces in the series like Nami and Rebecca have several differences (mainly the hair) that make them distinct. Brook is as tall as Aokiji, has the same facial structure, and has the same hair style. The only difference is that Aokiji is bulkier, which he SHOULD be since he used to be in the Marines.
- Brook's elemental affinity is Ice.
- Brook died TWO YEARS before Aokiji was born
The only major difference is that Brook has a very regal appearance, while Aokiji as a child has been depicted as being poor.
That's because after Brook passed away, his home island got destroyed by pirates. This is why Aokiji is so sympathetic towards Robin. It's because they parallel each other, and because his island was destroyed like Ohara. The only difference ism Aokiji's island was destroyed by pirates, and the Marines saved him instead (kind of like what they did with X-Drake).
This could also explain how Aokiji doesn't know Brook is his grandfather. He never got a chance to meet him, perhaps never got a chance to ever be told about him.
All this is a theory but I wouldn't be surprised if it's true in some capacity.