SPOILERS
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The King is the ML and the reason he hates gaudy women is because he was sexually assaulted (raped) by an older female teacher. In the original timeline the heroine didn't appear and the 10 concubines had traits of the heroine.
In this timeline he becomes interested in her because she bakes and he ate a cookie that she gave to her brother. He gets intrigued and thinks she's more complex than he assumed. Things happen and he gets obsessed with her and won't break off the engagement. There's a spoiler thread on novelupdates for more information but that's kind of the gist of it.
Ok I was not expecting the rape part but it did end up being the typical I want you now that you don't want me plot...
I don't have the patience to read through this extremely cliché plot. This might've worked 30 years ago but right now it feels extremely childish.