Hardest mate in 1 puzzles

Try to find it. Here's the answer, highlight to read
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But how do you know black's last move was ...f7-f5?
Dude, you have to figure that out. Otherwise how can you do the mate?
PS. Why did you show my solution?!!
I contend that your problem has no solution. That is why I did not bother to hide it.
Say you walked into a room and two players were playing this position. They've told you it's white to move. Isn't it far more likely that Black's last move was something OTHER than ...f7-f5?
hey the en passant is illegal because any move i play is incorrect. i think u forgot to add the en passant. add it or else the puzzle is unsolvable

This one is very hard....
Rather too hard. It has no solution, as en-passant is not allowed in this position by the official Chess Compositions Codex.
You can also add that the initial position is illegal.