  The LHCb Collaboration has recently discovered a structure around 6.9 GeV in
the double-$J/\psi$ mass distribution, possibly a first fully-charmed
tetraquark state $X(6900)$. Based on vector-meson dominance (VMD) such a state
should have a significant branching ratio for decaying into two photons. We
show that the recorded LHC data for the light-by-light scattering may indeed
accommodate for such a state, with a $\gamma \gamma$ branching ratio of order
of $10^{-4}$, which is larger even than the value inferred by the VMD. The
spin-parity assignment $0^{-+}$ is in better agreement with the VMD prediction
than $0^{++}$, albeit not significantly at the current precision. Further
light-by-light scattering data in this region, clarifying the nature of this
state, should be obtained in the Run 3 and probably in the high-luminosity
phase of the LHC (Run 4 etc.).
