We report a mode hybrization between the ferromagnetic resonance (FMR) and re-entrant cavities. These cavities were elaborated by a commercial stereolithography 3D printer and then a conventional 3D metallization procedure of plastic elements was used to produce a full metallization of copper and tin. The total volume was divided by 15 compared to a cavity in standard geometry resonating at the same frequency, while maintaining a high Q factor, in very good agreement with the simulations. In this article, we demonstrate the opportunities offered by 3D printing for the realization of complex 3D cavity geometries while highlighting an effective coupling of 40 MHz measured at room temperature. These experimental findings reveal a potential for the development of a new class of tunable filters based on a complex architecture of 3D printed cavities.