  A future Galactic Supernova (SN) explosion can lead to a gamma-ray signal
induced by ultralight Axion-Like Particles (ALPs) thermally produced in the SN
core and converted into high-energy photons in the Galactic magnetic field. The
detection of such a signal is in the reach of the Large Area Telescope aboard
the \emph{Fermi} Gamma-Ray Space Telescope. The observation of gamma-ray
emission from a future SN has a sensitivity to $g_{a\gamma}\gtrsim 4\times
10^{-13}$ GeV$^{-1}$ for a SN at fiducial distance of $10$ kpc and would allow
us to reconstruct the ALP-photon coupling within a factor of $\sim2$, mainly
due to the uncertainties on the modeling of the Galactic magnetic field.
