Abstract: The characterization of singularities inside black holes is a fundamental problem in General Relativity. While the celebrated “mass inflation” scenario suggests that a weakly *singular* Cauchy horizon forms inside generic black holes (near time-like infinity), the global structure of the black hole interior boundary has largely remained unexplored. I will present my recent proof that, in the context of the spherical collapse of a charged scalar field, the weakly singular Cauchy horizon breaks down in finite retarded time and gives way to either a r = 0 “crushing type” singularity, or a locally naked singularity emanating from the center of symmetry.