The king died. The crown prince succeeded, Beth was the crown princess. So now they are the royal couple. David is the son of a duke (I think), and is also Beth’s brother.
David’s father told him he should have a good relationship with Hue and become acquaintance but Hue couldn’t care less about nobility so he pays no mind to him and basically ignores him.
Then David dislikes Hue because he is a spoiled brat and can’t comprehend the fact that he needs to have a good relationship with Hue but Hue doesn’t need him.
Factor that the crown prince ONLY succeeded safely because of Hue’s support. That’s it.
What's going on... David is crown prince? Beth is his sister (who wanted to invite lucia to luncheon)? She's the queen? The king is the father? They both are Lucia's siblings?