Again, this trick is in fact really simple, that's why I like it. Most people will not think it out themselves.|
Here is the explanation.
When you hold the deck behind your back, you will turn the card which is on top of the deck.
When you show the bottom of the deck to the spectator (with the king of spades on the bottom), you will be able to see which turned card is on the top of the deck (a 10 of spades).
After taking the deck behind your back again, you will take the turned card on top of the deck (10 of spades), turn it and put it on the bottom. At the same time, you will turn the next card which is on top. When you show the deck to the spectator with the predicted card (10 of spades) on the bottom, you will be able to see the next card (ace of spades).
Please see video how you can do this.