The mixer (83) of the mixer-cartridge assembly comprises a housing (84), an inlet section (85) having an individual inlet (87, 88) for each outlet (33, 34) of the cartridge (30) and a mixer element group (3). The mixer inlet section comprising separating means (3S) and the mixer element group (3) are arranged thus, that while sealingly connecting the mixer to the cartridge, the inlets (87, 88) of the mixer remain aligned with the corresponding and matching outlets of the cartridge as well as with the separating means (3S) and with the dividing element (3D) of the mixer element group (3) for optimizing the mixing of the components. For mixer attachment, the mixer housing comprises bayonet lugs (89) cooperating with bayonet prongs (15) on the cartridge, whereby the housing is rotated while the mixer inlet section, separating means and element group do not rotate in regard to the cartridge outlets, thus avoiding cross-contamination of the components at the cartridge/mixer interface and assuring continued separation well into the mixer up to the first dividing element (3D).