  We present the results of a large multi-wavelength follow-up campaign of the
Tidal Disruption Event (TDE) \dsg, focusing on low to high resolution optical
spectroscopy, X-ray, and radio observations. The galaxy hosts a super massive
black hole of mass $\rm (5.4\pm3.2)\times10^6\,M_\odot$ and careful analysis
finds no evidence for the presence of an Active Galactic Nucleus, instead the
TDE host galaxy shows narrow optical emission lines that likely arise from star
formation activity. The transient is luminous in the X-rays, radio, UV and
optical. The X-ray emission becomes undetected after $\sim$125 days, and the
radio luminosity density starts to decay at frequencies above 5.4 GHz by
$\sim$180 days. Optical emission line signatures of the TDE are present up to
$\sim$250 days after the discovery of the transient. The medium to high
resolution spectra show traces of absorption lines that we propose originate in
the self-gravitating debris streams. At late times, after $\sim$200 days,
narrow Fe lines appear in the spectra. The TDE was previously classified as
N-strong, but after careful subtraction of the host galaxy's stellar
contribution, we find no evidence for these N lines in the TDE spectrum, even
though O Bowen lines are detected. The observed properties of the X-ray
emission are fully consistent with the detection of the inner regions of a
cooling accretion disc. The optical and radio properties are consistent with
this central engine seen at a low inclination (i.e., seen from the poles).
