An electro-optic mirror reflective element for a rearview mirror assembly for a vehicle includes a front substrate and a rear substrate. A surface of the front substrate and a surface of the rear substrate oppose one another and are spaced apart by a perimeter seal, with an electro-optic medium disposed between the surfaces and bounded by the perimeter seal. A transparent electrically conductive coating is established at the surface of the front substrate, and a specularly reflective mirror reflector is established at the surface of the rear substrate. The specularly reflective mirror reflector includes a stack of thin film layers having (i) an environmentally stable electrically conductive metallic reflecting thin film layer including chromium, (ii) an environmentally vulnerable electrically conductive metallic reflecting thin film layer and (iii) a transparent electrically conductive thin film layer including aluminum doped zinc oxide.