They don't live together and Lex didn't know of Krest till things started to happen. The king and queen(parents) must've known he was going to be evil. So, that's why they had gave him away to another royal kingdom, which is across the ocean. Now the kingdoms are fighting because one thinks the other is trying to destroy the other. Krest is next in line to be king. The kingdom though, is shrouded in darkness, unlike Lex's crystal kingdom.
Human form~
Shadow Demon form~
Refs~
