King not wanting anyone to know he's a Lunarian would explain his very reserved nature.
No one on the Beast Pirates has seen his face. He likely doesn't trust a single one of them, which would include Queen, who he glared at for mentioning his race. Kaido being the only real exception.
The only Beast Pirates who probably do know what he looks like are Kaido and possibly Queen. Kaido and King were experiments for the Government together, and Queen once worked alongside Vegapunk, who's affiliated with the Government. He's also displayed the most knowledge about Lunarians, which would make sense if he had access to notes or was involved in the research. Kaido likely recruited the two together.
King's animosity towards Queen could be explained by the experiments he probably had to endure under him. A Zoro and Sanji bromance these two don't have. There's no doubt in my mind they despise each other more than anyone else.
