Merlins of Wakefield - It's always magic at Merlins

You show your audience three playing cards, say, two black tens and a red king. The red king is between the black tens. The fan of three cards is turned face down and the middle card (king) can be seen to have a totally different coloured back. Very cleanly and slowly you separate the middle card and place it face down on the table. The two remaining cards are placed to one side. When the spectator turns the king over it is totally BLANK! Perhaps they suspect that you are using extra cards? You are, but smaller than they expect, you spread the two black tens and there between them is the red king but now it has diminished to half its original size!