Bound to the enemy

Kylian is the son of Satan and the next ruler of hell. He ran away from home and is now hiding above ground to hide from his fathers enforcers that are after him.
Silas, a human born into high class, but one horrific night changes his and his twin sisters life for the worst.
Somehow these 2 different species are bound. There's just one problem...they despise each others guts. Its only natural, vampires hate demons, and demons hate vampires. They both have been at war since the begining of time.
Kylian thinks its a curse from his father for not taking his place on the throne. Silas believes its from the moon goddess, punishing him for what he has done in the past.
How can a demon and vampire fall in love? let alone befriend each other?
Maybe this whole thing is a curse, or perhaps a blessing.