I think this is the old artist of Why Would a Villainess Have Virtues?
https://www.mangago.zone/read-manga/why_would_a_villainess_have_virtue/
i believe the twitter is legit but I don't think this Instagram account is. It's in English, they follow 4 people who are not Korean and have very little following. Also, it's not up to the artist to deal with lawsuits and illegal reproductions of their work. It's the publisher who deals with those type of issues.
It's been a bit since I've read the novel but
The manga is taking a completely different direction compared to the novel but the prince should still not be the ml. In the novel Astrid develops feelings towards the high school teacher later on and marries him after she finishes school. In the novel she's already a middle schooler I believe and makes a club for blood magic or something and he's the sponsor for it. This could be somewhat incorrect as I haven't read it in a couple of months ╮( ̄▽ ̄)╭
that last panel of him smiling got me blushing (づ ̄ ³ ̄)づ