The world's best card trick

This is a pretty cool trick.A card is freely selected from a pack of cards.That card is put into the middle as per the wish of the spectator.Now a different backed card mysteriously appears in the deck and is shown to be the spectators card and is kept right in front of the spectator.(Wait,the trick's not over yet.)Now the spectator is asked to pick another card(free choice) and is asked to remember this card.Now, when this card is put backed into the deck and when everyone is waiting for a different backed card to appear(as before),it doesn't.But the card which was revealed first(spectator's first selection) has magically changed into the spectators secondly chosen card.Luks really IMPOSSIBLE!!