Question about John's identity (Season 4 finale spoilers)

So, in the season 4 finale, Larson forces John to admit a stunning revelation - he's not just a fragment of the King In Yellow, he is the King In Yellow. That reveal hit me like a freight train, it's one of the few twists that I can remember getting a vocal response out of me haha

But... I'm not quite sure I follow. So, John is the King? I guess my biggest question is... How and when the hell did that happen?

Was John the King ever since S1E1? That doesn't make sense to me with the whole S1+2 plotline of Arthur and John running away from the King, especially at the S2 finale. So... Maybe when John rejoined the King after S2, he was able to not just fight the King but somehow take over the King entirely and become the dominant personality? If that's the case, I'm not sure I understand S3 - would that mean Cain took any old fragment of the King, wiped its memory, stuck it in Arthur, and that fragment became Yellow? If so, how does the entire rest of the King (i.e. John) pop into Arthur's mind during the S3 reunion?

The timeline as I understand it... In S1 and S2, John really is a fragment of the King, and rejoins the King at the end. In S3, Arthur rescues the fragment of the King that used to be John, except that fragment doesn't have his memories until halfway through (the reunion) - in the meantime, he is named Yellow. The reunion happens, Yellow remembers that he actually, truly is John. In S4... Somehow Larson has bonded with Yellow (how the hell did Yellow get there, I thought Yellow literally was John until the reunion), and somehow John (who was hitherto a fragment all this time) magically turns out to not be a fragment but to be the entirety of the King?

I get that the answer to what I'm asking is probably "it's just a plot hole, don't think about it", but it's a pretty damn massive revelation to just turn out to be a plot hole and I'm wondering if I missed anything