Okay just found I saw this on spoilers page who said this entire story based on a historical book excerpt from s1 side story
I copied the comment
“The story about Alexandra and Cyril was mentioned in the novel in a form of historical book entry around 1 paragraph, something like “there was this knight lady who was at some point romantically pursued by the young king over a decade younger than her. At some point she gave in and became his queen and they ruled happily ever after”. So all the events in the upcoming manhwa will be original.”

How is the romance gonna pan out cause the Cyril that is in this era is young but the Cyril that she fell for is from the future