Considering the sheer amount of running this guy does in all of his movies, as well as the commitment he brings to his stunt work (which recently led to a leg injury on Mission: Impossible 6), it’s possible to imagine that this could be a legitimate shot of a legitimate butt.
Having established both sides to this debate, if any Hollywood actor has a chance of possessing a butt with those specific, Kardashian-esque proportions, then Tom Cruise seems like a solid bet.
Even at age 55, the guy continues to keep himself in excellent shape, and the action icon was only in his mid-40s at the time of Valkyrie’s release.