cannot occur on board 2, because it would mean king and rook moved).
Moreover, the king cannot be in check on board 2 after castling.
+h3 Note
+
+p.
+ Any move played should be legal on the board it is done,
+ and result in a legal situation on the other board. For example
+ 1.Pe4 Pd5 2.Be2!? Sxe4?? 3.Cb5# is checkmate because
+ 3...Kd7 is not valid on board 1.
+
h3 End of the game
p.