THEY ARE BOTH ASRIEL'S KIDS (no pun intended) BY BLOOD, AND THEY WERE BORN AND RAISED TOGETHER AS SIBLINGS



THEY AREN'T UNRELATED IN TERMS OF DNA , AND THEY WEREN'T INTRODUCED TO EACH OTHER AT A YOUNG AGE, T H E Y. G R E W. U P. T O G E T H E R. A S. B L O O D - R E L A T E D. S I B L I N G S.