A three-piece modular aerosol-generating device, including: a mouthpiece including one first connection element at a distal end of the mouthpiece; a functional component including an air inlet and a cavity to receive a consumable; and a main body, the component being arranged between the mouthpiece and the main body and further including one second connection element at a proximal end and one first connection element arranged at a distal end, the main body including one second connection element arranged at a proximal end of the main body, the first and the second connection elements being connectable to each other and providing mechanical, electrical, and hermetic coupling, the first connection elements including an annular recess and the second connection elements including a tubular protrusion, or vice versa, the annular recess being to receive the tubular protrusion, and the annular recess and the tubular protrusion having matching shapes.