in lover avenged, it is revealed that the princess in rhev's half sister...really? 由 blood 或者 as a fellow symphath? he's going through enough hell without adding incest to the mix.
They are brother and sister 由 blood through their father who was the Sympath king. Although the princess is full sympath Rhev is half vampire through his mother who was raped 由 the king.
Rehv and the Princess share the same father, Rehv's mother, a fallen chosen, was raped before she married Bella's abusive father. This added dynamic, (incest) helped make Rehv sacrifice for his family that much greater.