Copyright APS. This version is available at http://link.aps.org/abstract/PRB/v76/e104431 We report on an x-ray resonance exchange scattering (XRES) study of multiferroic TbMnO3. Magnetic scattering is observed close to the Mn K edge and the Tb LIII and LII edges. Surprisingly, Tb shows XRES also in the paraelectric phase, where neutron diffraction results suggested the 4f moments to be disordered. The temperature dependence of the XRES intensities shows a distinct kink close to the ferroelectric transition temperature TC for all absorption edges. We were able to model the temperature dependence for all edges, assuming a strong coupling of Mn and Tb magnetism via the spin polarized 5d conduction band. We argue that the hybridization between Mn and Tb states is a prerequisite for the multiferroic effect in this material. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Science, under Contract No. W-31-109-Eng-38. The MUCAT sector at the APS is supported by the Department of Energy, Office of Science through the Ames Laboratory contract No. W-7405-Eng-82.