We consider the photon pair production at the next-to-next-to-leading order (NNLO) in perturbative QCD at the LHC, taking into account for the first time the full top quark mass dependence. We present the computation of the two-loop form factors for diphoton production in the quark annihilation channel. We discuss the relevant scalar integral families for the process and the master integrals (MIs) are evaluated by means of differential equations. Finally, we discuss the phenomenological results showing the relevant ratios of the fully massive computation with respect to the massless ones.