What is the missing piece (marked "?") in this configuration of a normal chess game?

BLACK

WHITE
Notice that the Black King is in check by the White Rook.

(In reply to re: An impossible check?? (partial spoiler) by Dej Mar)

Dej Mar,
What you say is totally true.

I was attempting to being too direct about "promotion" of the piece, hence my bold ' "on" the board ' reference; the pawn used is not on the board.

Additionally, as for "Very good observation, brianjn", I cannot take fully credit for that.  pcbouhid originally had this as a text diagram, I offered to build it as a picture but in doing so I made a noticeable error which, when drawn to my attention, I rectified.  Later I saw that "glaring mistake" asked pcbouhid to reassure me that the picture was indeed correct.  His reply was to "focus on the other Rook".

It took quite some time before I realised that the discovered check was due to the promotion of a pawn; well, that "very good observation" was somewhat assisted.  With that in mind I felt I couldn't give too much away - "inside information" so to speak.

Edited on June 12, 2008, 8:51 pm

Posted by brianjn on 2008-06-12 20:27:35