user7623: I'm playing as white against a cpu. Black has a knight on A7, which he moved to D4 to capture my queen. How is this possible? I've been playing chess for almost 20 years and I have never seen ir heard of this move. Is this a special knight move? What is it called?

user86: Without further context, I can simply say that the move you described is not a legal knight move in any position or circumstance. It is, however, a legal move for a bishop. Perhaps you mistook the bishop for a knight.
If you could supply the PGN of the game, it would clear up some confusion.

7623: <p>I'm playing as white against a cpu. Black has a knight on A7, which he moved to D4 to capture my queen. How is this possible? I've been playing chess for almost 20 years and I have never seen ir heard of this move. Is this a special knight move? What is it called?</p>
 86: <p>Without further context, I can simply say that the move you described is not a legal knight move in any position or circumstance. It is, however, a legal move for a bishop. Perhaps you mistook the bishop for a knight.</p>

<p>If you could supply the PGN of the game, it would clear up some confusion.</p>
