Mind Bender

A young boy is playing against his friend on a standard chess board. It is his turn to move. After thinking for a few seconds, he smirks, then picks up his king and moves it to the other side of the board. His opponent glances at the position with astonishment, yet does not call it an illegal move. Instead, he resigns. How is this possible?

Answer below!

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They are playing checkers. The little boy's "king" jumped over many of his opponents' pieces to reach the other side of the board. Not having seen this possibility, his surprised friend resigned accordingly.