because even in her previous life she had'nt seen him cause like he does'nt come to all the banquets and stuff being organized. she says it herself though...
Spoiler alert
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In the previous life the prince has no power against the aristocrat party and he's very much like a puppet and under his fiancee's control. He couldnt do anything because he was frequently framed and the enemy keep on trying to destroy his name. Which makes him unable to hold his head high in front of his people. Since meeting aria he got a lot of help since aria is indeed knowledgeable and that helped the prince to evade some of the stuff that supposed to destroy the prince.
Isn't the black haired dude the prince? Why doesn't Aria know him from her previous life?