Congratulations to Maximiliast on the victory!
I went from playing spoiler to the RD to being spoiled myself!
Earlier in the game, I kept looking at the LI and DK as I had both their capital locations under constant recon. I figured I'd fight one of them, but then the RD got three regions, then four! don't know how close the RD was to victory, but I was divining his army groups, and when I saw four in Crown Islands plus four regions, I feared the worst. I felt I had to move, even though I wasn't really ready. However, things went really well in the Sword Coast, and Zamora was a small and easy-to-take region. I was not actually trying to win, but suddenly I found myself with four regions and a whole lot of enemies!
In hindsight, I should have picked up part of the Sword Coast and Zamora, but not control, to allow myself to get into a better position for the long game. At the time, I wasn't thinking that, though; I wanted to make sure the RD didn't win. I was chased out of Sword Coast and then Zanthia by multiple kingdoms. I tried to consolidate and take the DK out of Nyvaria and Untamed, but his pop centers just had no people left! At one point, I had nearly everything in Nyvaria, but the city and his capital, and it still wasn't enough for regional control! The DK also played it well and quickly wised up to my use of invisible groups, moving to retake things immediately, where normally there would be a delay. It didn't help that my groups were never a match for his, and also couldn't take legendary PCS. If I did it again, I'd do more to build a more robust group rather than have multiple modest armies (though the invisibility is nice).
And it didn't help, I thought the game had ended and missed a turn there in the late game! Oops