Building on family systems theory and lifespan views on aging, the present study investigates how the experiences of grandchild-related bliss (i.e., the subjective fulfillment and joy of having a grandchild) are related to grandparental couples' partnership-related and general well-being. We hypothesized both (a) actor effects (i.e., a grandparent's grandchild-related bliss is positively associated with this grandparent's well-being) and (b) partner effects (i.e., a grandparent's grandchild-related bliss is positively associated with the partner's well-being). We used the actor-partner interdependence model to distinguish these kinds of effects. The data were collected at two measurement time points, which were 4 weeks apart. The sample consisted of 163 heterosexual grandparental couples who cohabited and had a first grandchild (up to 8 years old). No actor effects were found for grandmothers. However, the grandfather's grandchild-related bliss was associated with the grandmother's reports on relationship quality and meaning in life (partner effects). For grandfathers, grandchild-related bliss was positively associated with their relationship quality, satisfaction with life, and meaning in life (actor effects). Unexpectedly, the grandmother's grandchild-related bliss was negatively associated with the grandfather's relationship quality (partner effect). These findings provide new insights into the gendered family experiences of grandparents and expand our knowledge regarding the psychological well-being of older romantic couples. (PsycInfo Database Record (c) 2026 APA, all rights reserved).