Kunis helped pick her own butt double

The sexy Black Swan star agreed to get naked opposite Justin Timberlake for the saucy new movie, but insisted the camera could only capture a little “side boob” – and no bum.

So she agreed to help the director and the casting director find her perfect body type from a line-up of gorgeous wannabes.

She says, “These young ladies came in and they were in a casting room and I was there with the director and the casting director… and these lovely women had to show us their derrieres and we chose the one that most resembled my body the most.”