In 2009, Calegari constructed smooth homotopy 4-spheres arising from an infinite collection of automorphisms of free groups including monodromies of fibered knots in the 3-sphere. We prove that all of these homotopy 4-spheres are diffeomorphic to the standard 4-sphere. Our result implies that the work of Casson and Gordon on homotopy ribbon fibered knots gives a large family of potential counterexamples to the smooth 4-dimensional Schoenflies conjecture. Our method builds on 5-dimensional handlebody arguments and the 3-dimensional Poincare conjecture. This is joint work with Jae Choon Cha.