Here are some recommendations for novels similar to The Mad Queen of Kings:
1. The Silly Emperor and the Crazy Queen: This novel may have similar plot and theme to The King's Crazy Queen.
Please note that due to the limitations of the search results, there may be other similar novels, but they are not mentioned in the search results.
Since I haven't watched the show in great detail yet, I can't say for sure who the king is. But considering the Bridgerton setting which draws from the Regency era, it's probable that the king is modeled after one of the Hanoverian kings. Given Queen Charlotte's presence, it might be George III as he was her husband in real history. However, the show may take some creative liberties with the character, so it could be a somewhat fictionalized version of him with added elements to fit the Bridgerton story.
The queen and the king are the central figures. There may also be other supporting characters like their servants, knights, or advisers who play important roles in the story. For instance, a loyal knight who protects the king and queen from danger, or a wise adviser who gives them good counsel in difficult situations.