So... initial position is
[FEN "7k/8/6KB/8/p7/8/Q7/8 w - - 0 1"]
Now... Neither white's king nor queen has moved in the previous five moves. In addition, no pieces have been captured by either side. What was the last move? Also, where the piece came from here?
Since the black's king can't move it's very tempting to say that black's last move was a pawn move or white's last move was a bishop move. The tricky part is the mention of 5 moves. Black's pawn can only do 3 moves from starting position, and since white's queen and the king didn't move, black's king is stuck.