  We present the results from a dense multi-wavelength (optical/UV,
near-infrared (IR), and X-ray) follow-up campaign of the nuclear transient
AT2017gge, covering a total of 1698 days from the transient's discovery. The
bolometric lightcurve, the black body temperature and radius, the broad H and
He I $\lambda$5876 emission lines and their evolution with time, are all
consistent with a tidal disruption event (TDE) nature. A soft X-ray flare is
detected with a delay of $\sim$200 days with respect to the optical/UV peak and
it is rapidly followed by the emergence of a broad He II $\lambda$4686 and by a
number of long-lasting high ionization coronal emission lines. This indicate a
clear connection between a TDE flare and the appearance of extreme coronal line
emission (ECLEs). An IR echo, resulting from dust re-radiation of the
optical/UV TDE light is observed after the X-ray flare and the associated
near-IR spectra show a transient broad feature in correspondence of the He I
$\lambda$10830 and, for the first time in a TDE, a transient high-ionization
coronal NIR line (the [Fe XIII] $\lambda$10798) is also detected. The data are
well explained by a scenario in which a TDE occurs in a gas and dust rich
environment and its optical/UV, soft X-ray, and IR emission have different
origins and locations. The optical emission may be produced by stellar debris
stream collisions prior to the accretion disk formation, which is instead
responsible for the soft X-ray flare, emitted after the end of the
circularization process.
