HI! HEADS UP.
I was VERY confused about these revelations earlier in the episode. I tried to edit this as clear as I can and stitch together what was actually coherent but I apologize if some thoughts were unclear/stopped abruptly. Just know the rest of that sentence or phrase was not coherent at all lol. I was going back and forth between clips and was verbalizing my thoughts as I went but none of them were actually making sense. BUT rest assured, I did end up understanding these revelations eventually before the ep ended.
SPOILER FOR THOSE WHO ARE WATCHING FOR THE FIRST TIME:
I think what confused me was the two names that were introduced to me earlier in the series. I'm totally thankful for everyone's comments to help me further understand the plots but I think the introduction of the white hair dude's two names without much context (understandably as it would've spoiled the plot), confused me overall.
Correct me if I'm wrong but I'm currently at this:
Qi Min = REAL heir to the throne (given the surname of the royal clan)
Sui Yuanhuai = Son of Lord Changxin (cause current heir brother has a very similar name)
But they're not technically synonymous with each other. They're two different people. My confusion stemmed from this. I thought white hair dude had the two names as THE SAME character (like how Xie Zheng is with Jiuheng - that one is a nickname). And I often used Qi Min earlier in the eps because it was just easier to pronounce without knowing the real reason behind that name.
So when Xie Zheng said "the real Sui Yuanhuai died 17 years ago", I thought the real heir to the throne died too so I was like who tf is this imposter then?? But no- it's just the real Sui Yuanhuai that died. Qi Min is currently the name of the person alive but just pretending to be Sui Yuanhuai. A switch that happened to keep him alive.
Gosh watch me be wrong on this too 😭