beta
It’s not the brother
The emperor/king the one who is very obsessed with him ,
After he die in their past life
The emperor/king committed suicide by jumping of on a cliff after that he was reincarnated a few time i think every time he draw his last breath he kept wishing to be with taehyuk to become his brother or something
( my only assumption) then after so long they became REAL BROTHERS .
In the Current timeline