For quite some time we’ve been trying to find out who Kaido's son Yamato, truly is from the One Piece Wano Country arc manga. In the latest chapter of the manga, which is Chapter 984, Yamato removed his mask to reveal something quite surprising to the fandom.
During the previous chapter, Yamato came out to help Luffy with Ulti and Page, and from there, he fought Luffy in a bid to have a word with our hero. By the end of the current chapter, Yamato removed his mask, but instead, there being the face of a man, it is instead a woman.
As it now stands, Kaido doesn’t have a son, but rather a daughter who chose a male persona for a particular reason. You see, she wanted to be like Kozuki Oden as he once opened Wano’s borders to everyone, but Kaido killed him for it.
In the end, Yamato chose to become a man because Oden, her hero, was a man. Whether or not Yamato will stay in this state is left to be seen, but we believe the author will allow it to be. We can only hope that Yamato shows up in future arcs after this one is over and done with, and that is coming very soon.