This scene is a combination of Natalie Portman and a body double. In the bottom row of the collage, the two pics on the left are Portman while the three on the right are a double named Caroline Davis. Davis was paid to dive into the freezing lake in Northern Ireland.
That’s some seamless doubling. Those two women look very similar.
Straw man o’ the day: some people have argued that it can’t be Portman at all because she was pregnant. This is an incorrect assumption based on the release dates of Black Swan and Your Highness. In fact, Your Highness was filmed between July and October of 2009, and Black Swan was actually filmed AFTER Your Highness, from December 2009 until February 2010. That means Portman had not yet even met her future husband when the Your Highness scene was lensed. Portman’s son was born in June of 2011.
I don’t know… I can see a difference. Portman’s ass is lovely but not as well rounded as the double.