I was playing a game against a level 1 computer just to hone my skills and test out some strategies. So, I made the move Nh4 and the computer responded with Kc8 from e8. I took a screenshot of the move but idk how to post it here. I'm not sure if this matters but the Black King hadn't moved the whole game, and the entire 8 Row was empty except for the corner Rooks that hadn't moved either. Am I missing an important rule here that allows the King to do that, I've never heard of it. Any help would be appreciated, thanks Chess community!
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