🧠 Confusing Ruy (Illegal Move Exercise)

Illegal Move Exercise: The audio will lead you through a series of moves from the beginning of a game. Somewhere in there, a player will make an illegal move but the game will continue anyway. Find the illegal move.

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PGN for today's exercise:

1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Nxe4 6. Re1 Nc5 7. Bxc6 dxc6 8.d4 Ne6 9. Nxe5 Bd6 10. c3 Bxe5 11. Rxe5 O-O 12. Nc3 Qxd4 13. Qh5 Qd7 14. Re1 Qe7 15. Be3 Bd7 16. Rad1 Rad8 17. h3 Bc8 18. Qf5 Nd4 *

And the answer is...
White’s move 12. Nc3 is illegal as the c3 square is already occupied by a White pawn (that was moved there on move 10).