Mongmong never had parents...there's a chance his sister is not his actually his...the Kims' child is dead or as they were told(?)...Jeha is a childhood friend of their child...yaoi's common theme are childhood friends turned lovers...mongmong is a potential lover...mongmong = the kims' child? hmmm
i was thinking the same so i went back to the story. mong looked kinda similar to the kim's son without his hair dyed, if it was more neat yk. but they also mention how he was an orphan since a newborn baby and they found him in a basket so that could also rule out the possibility and mong has no memory of ever losing it or anything. i would love for this one to be true though so if we get more of jeha's backstory, we can see if it leans more to this theory!!
He's all just a dick really. The only thing he's good for.