Responses
I think (this is just my thoughts) that the queen wants the prince to feel loneliness and ended up depending her like how his mother is. But the poison and all is the concubine's fault, to kill Saphir. So basically, queen= kills people around Saphir so he'll be dependent on her, the concubine = wants Saphir to die
That makes sense!
I wonder if it really is the empress who sent assassins or her son the crown prince. Because in an earlier chapter she wants to send someone from a higher brigade to search for Saphir when he disappeared, but the crow prince vetoes it and say something along the lines of favoritism.
Maybe its even another concubine who hated the fact that Saphir's mom, a commoner woman, earned both the favor of the emperor and the empress, seeing how those prince and princess were so comfortable mistreating him.