  We follow up on our discussion of the exact quark-mass dependence of the
Higgs-gluon form factor at three loops in QCD (arXiv:2001.03008) and turn our
attention to the closely related Higgs-photon form factor. Similarly to our
previous work, we intend to examine the form factor for the decay of a
Higgs-boson with variable mass into two photons at the three-loop level in QCD.
The set of master integrals is known numerically due to prior work on the
Higgs-gluon form factor and is exploited to obtain expansions around the
threshold as well as in the high-energy limit. Our results may be utilised to
derive the photonic decay rate of the Higgs-boson through
next-to-next-to-leading order.
