Just a plot twist I guess. For the drama.
cause he doesn't wanna live anymore? ike he lost the will to live
It's because they are afraid that he might gather enough forces to retrieve the throne. He is known as a tyrant, someone who baths their selves with power and blood.
Yes, This and also maybe because they want the commanders prove of loyalty towards the new imperial court/king.
I'm confused, why was he killed? I thought he was just exiled