Moon phase display mechanism including a control wheel driven by a movement, which control wheel drives a moon phase disc behind an aperture in a dial, and this mechanism includes: coaxial, superposed and permanently driven in opposite directions, a first phase indicator wheel carrying a first heart cam, and a second phase indicator wheel carrying a second heart cam, and this control wheel includes means for guiding a double lever comprising two arms, only one of which arms is arranged, at any time, to cooperate in contact with one of these second and first heart cams, each to display the moon phase visible in either the Northern or Southern Hemisphere, and to allow the moon phase disc to pivot in the appropriate direction for this hemisphere.