Watt??

It is the 'real' Min Siwoon (who is terminally ill). which is why he says that it will be Min Woojin that dies when he does, because he will have to taker over the role of the heir his 'fathers' company and leave his old identity behind as though he never existed. Which is why is so heart breaking because both of the main characters have been forced to abandon their childhood identities, but have miraculously been reunited against all odds.

Poor Min Siwoon T~T..