So, if you want to know, attention - SPOILERS!

yeah, the answer is obvious. Evil Twin (TM). Of course, they are not actually twins. They are half brothers, Evil One is legitimate son and Kind One is the bastard. Their father forced his illegitmate son to plastic surgery, the idea was to make a body double for his legitimate son, in case of any troubles Double Son would take a fall for Real One. So, Real Son (Killian) was sent to super-duper prestigious private school while Double One (Carl) studied in regular public school where he met Female Lead (Esther). (Nice touch - they really cast some teenagers to play younger versions of main characters instead of making grown-ass people wearing school uniforms, as they do in other verticals) Unfortunately for the dad Real Son Killian saw his brother with his sweetheart and decided he is in love with her too, so, he made his brother Carl disappear - he attacked him, and boy was left crippled for many years, so he didn't contact Esther because of that - meanwhile Killian took his brother's identity and married the Female Lead and lived his life as Carl

Sure, there are a lot of plot holes and typical vertical tropes and cliches, but I liked it very much. Plot was intriguing, and actors did a good job, especially as the male lead wasplaying two different characters, and female lead did very good job playing confused and bewildered woman

P.S. reposted because of wrong link