The oldest brother. I kinda forget tho, but one thing is sure, because envy, i guess.
I knew it the first time I saw him. Those who mc think is a good person almosy always turn out to be the bad guy.
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Spoiler
It was the first brother. Actually none of them is the son of their dad they were all adopted when there were a baby. I think he killed him because he has more responsibility and he wanted more money etc...
Li Zhenran knew that from the start (that they are not step brother) and helped him without him knowing expose the truth
*Possible spoiler*
Please someone who had read the novel tell me who murdered him and the reason behind it （￣へ￣? Why was he killed?