What happened to Jae Hyuk in Immortal Regis to Cavalier Of The Abyss?

in Cavalier Of The Abyss n jae hyuk turns out to be the EVIL n i mean EVIL king. n serin SUPPOSIBLY betrayed him. k wat i dont understand is that at the ending or immortal regis jae hyuk brother was taken away n jae was going to rescue him. jae hyuk was a SWEET, CARING, OUT GOING, GREAT boy n look wat happened to him it BROKE my heart. he turned into a RUTHLESS killing machine he even kills HELPLESS kids. dosen't care about anyone NOT even his own FAMILY. in the 1'st season he was SWEET but now he is a ***** he aint the main character anymore and the story takes place like 30 YEARS later wen jae has a wife n 2 kids. wat did it skip the part about him being good n rescuing his brother n living happy together. CAN SOMEONE PLEASE PLEASE PLEASE get my story straight because im TOTALLY CONFUSED. did he save his brother and why skip all the good parts please tell me he is gonna turn BACK to how he used to be a gentle funny and caring person n not some BEAST. n is he gonna become a good king n help ppl again n is he and serin gonna get back together THIS IS ******* crazy i cant believe the author made the book this way someone tell me OTHERWISE