The first heterometallic copper-cerium polyoxometalate, [{Ce-IV(OAc))Cu-3(II)(H2O)(B-alpha-GeW9O34)(2)](11-) (1), is composed of an unprecedented copper(II)-trisubstituted Weakley-type tungstogermanate subunit stabilized by coordination of a {Ce(OAc)}(3+) group at the vacant position. The title species contains a central {(CeCu3O18)-Cu-IV-O-II} rhomblike cluster that belongs to a new {(4f(ext))(3d(ext))(3d(int))(2)} type and magnetically behaves as a triangular Cu-3 system with overall antiferromagnetic exchange affected by the structural distortions the vicinity of diamagnetic Ce-IV induces.