Royal Transposition (Stage)

Two giant cards (8×12 inches) are shown and then put into two empty drawstring bags of different colors. The Queen of Hearts is put into a red bag and the King of spades into a black one. After a magical gesture the two giant cards are taken out of the respective bags but… they will have magically changed places: the Queen will be taken out of the black bag and the King from the red one.

At the end you could explain it was all an optical illusion as you are using two kings (or two Queens) which can be shown front and back