His sibling (twin) probably died and got absorbed by his body.
His parents were biological siblings, twins actually so they gave birth to twins with defects. He absorbed his twin
Which doesn’t seem right, not just because it is incest but because families who are known to have twins, it generally skips a generation.
It's just the fetus development are not completely separate during kinases which make the twin are glu together.. it's just simple science
Woah a ghost baby on ur back.. that's scary.. but how did he got that..