A fan blisk for a turbomachine, the blisk comprising a hub delimited by an upstream face and a downstream face in addition to an outer peripheral face and a revolving inner peripheral face delimiting an inner opening, the hub carrying blades each having a leading edge and a trailing edge, the hub and the blades forming a one-piece assembly. The upstream face and/or the downstream face is offset, being located along the axis of rotation (AX) between the leading edges and the trailing edges of the blades, the blisk (bladed disk) comprising a filling member mounted on the offset face, the filling member comprising an inner centring ferrule engaging in the inner face of the hub, a radial portion resting against the offset face and an outer ferrule extending the outer peripheral face of the hub.