  3C318, a radio-loud quasar at z=1.574, is a subgalactic-sized radio source,
and a good test-bed for the interplay between black hole and galaxy growth in
the high-z Universe. Based on its IRAS, ISO, and SCUBA detections, it has long
been considered as one of the most intrinsically luminous (L$_{\mathrm{IR}}$ >
10$^{13}$ L$_{\odot}$) infrared sources in the Universe. Recent far-infrared
data from the Herschel Space Observatory reveal that most of the flux
associated with 3C318 measured with earlier instruments in fact comes from a
bright nearby source. Optical imaging and spectroscopy show that this
infrared-bright source is a strongly star-forming pair of interacting galaxies
at z=0.35. Adding existing Spitzer and SDSS photometry, we perform a spectral
energy distribution analysis of the pair, and find that it has a combined
infrared luminosity of L$_{\mathrm{IR}}$ = 1.5 $\times$ 10$^{12}$ L$_{\odot}$,
comparable to other intermediate-redshift ultra-luminous infrared galaxies
studied with Herschel. Isolating the emission from 3C318's host, we robustly
constrain the level of star formation to a value a factor of three lower than
that published earlier, which is more in line with the star formation activity
found in other Herschel-detected 3CR objects at similar redshift.
