<p>We investigate theoretically a nuclear excitation mechanism involving absorption of non-resonant photons leveraged by the coupling to the atomic shell. The nuclear non-resonant photoexcitation is assisted by electron recombination, which compensates the energy mismatch between photon and nuclear transition energies, reminiscent of parametric up-conversion in non-linear media. This third-order process proceeds via a virtual nuclear state—rather than virtual electronic states—distinguishing this mechanism from the electronic bridge. We investigate the process on the example of a so-far not observed 14.2 keV hard X-ray transition in ¹⁹³Pt driven by an X-ray free-electron laser. Although the calculated cross section is small, it can be compensated by the vast number of non-resonant photons from the X-ray laser pulse. By enabling nuclear excitation through non-resonant photons, this up-conversion-like mechanism suggests new directions for non-linear X-ray interactions mediated by nuclear transitions.</p>