That was a weird and confusing convo between the Prince and Elena when she introduced herself. :/
For one, how can she be part of a knight order? Since she went back in time I do not think she actually belongs to any order, though I suppose for simplicity's sake - and to avoid the awkward situation of having to explain her unique circumstances - she could have just counted herself as part of her family's knighthood .
For two, and to make my first problem even more perplexing, how could the Crown Prince have known her name just by hearing which order she supposedly belonged to? Does he also have memories from the first timeline? But if so, why didn't he remember when and how he was assassinated?
Well, my best guess at this point:
Elena fibbed about being a knight in an order to give a plausible explanation for her skills, and I think the Prince might really remember just possibly didn't have any/much time to prepare because the time reset happened to too soon before the assassination attempt. After checking the same scene in the novel version , I'm getting the impression that when Elena said that she was of the Fourth Order of Knights she simply meant she was from the family that was the commander of it, and the Crown Prince recognizing her might have had something to do with his dragon abilities. But the novel is not much clearer, so...
Seriously, while I generally enjoy this manhwa very much, the way the story is presented to us is way too full of unnecessary plot holes sometimes