Mate in 1? But harder than you think...

Just look at this picture. Can you find a mate in one?

Yes? Is it a checkmate for sure? Or do you think it's impossible?

Then let's see!

Would you move to c8 with the white rook? This cannot be mate in one move, because the black king can capture the white knight. (However, it can be a mate in 2) Let's just see:

But what if we play knight to c6? Is it a checkmate? No. In this position the black king can simly captures the white rook :

So: not a knight move, not a rook move... We can not check the black king   with the queen .... If we move wit the pawn , that will not be a mate either....

However I started this challenge by asking: can you find a mate in one? IS there any mate in one? Yes. Becouse I've never told you whose move it was. It's not white's move. It's black's move. How can we do that? Look at the picture again! Can you find it now? Yes? Or no? Then I'll show you:

THAT IS A CHECKMATE IN ONE!

Did you find it?

Tell me in the comments!