In the past, the emperor took an arrow in the back for Chengxu. That damaged his lungs, which is why he has been coughing a lot recently. He probably dies from that.
Goyoolee:
That is so freaking dumb. They don’t even do a one time hook up or have a fling after the emperor dies????? Why is the kid emperor such a dumbas_s? Assuming his dad dies when he’s young, shouldn’t he have better character since Mingyu is his mom? You would think.
Didn’t the spoiler also say that Mingyu’s kid dies and Mingyu helps another kid become emperor?
and yes, in the spoiler, it does say Mingyu's grandchild will become emperor. He probably doesn't have a "better character" because, in the spoiler, he was forced to marry someone he doesn't love, who is probably Yang Chao Yue's character.