  This Letter reports evidence of triple gauge boson production $pp\to
W(\ell\nu)\gamma\gamma + X$, which is accessible for the first time with the 8
TeV LHC data set. The fiducial cross section for this process is measured in a
data sample corresponding to an integrated luminosity of 20.3 fb$^{-1}$,
collected by the ATLAS detector in 2012. Events are selected using the $W$
boson decay to $e\nu$ or $\mu\nu$ as well as requiring two isolated photons.
The measured cross section is used to set limits on anomalous quartic gauge
couplings in the high diphoton mass region.
