  XDCP0044.0-2033 is the most massive galaxy cluster known at z>1.5 and its
core shows a high density of galaxies which are experiencing mergers and
hosting nuclear activity. We present a multi-wavelength study of a region
located 157 kpc from the center of this galaxy cluster, for which we have
photometric and spectroscopic multi-wavelength observations (high resolution
HST images in F105W, F140W and F160W bands, NIR KMOS data in H and YJ bands and
Chandra ACIS-S X-ray data). Our main goal is to investigate the environmental
effects acting on the galaxies inhabiting this high density region. We find
that the analyzed region hosts at least nine different sources, six of them
confirmed to be cluster members within a narrow redshift range 1.5728<z<1.5762.
These sources form two different complexes at a projected distance of $\sim$13
kpc, which are undergoing merging on an estimated timescale off 10-30 Myr. One
of the sources shows the presence of a broad H alpha emission line and is
classified as Type 1 AGN. This AGN is associated to an X-ray point-like source,
whose emission appears moderately obscured (with intrinsic absorption $N_{H}
\sim 10^{22} cm^{-2}$) and hosts a relatively massive black hole with mass
$M_{BH} \sim 10^{7} M_{\odot}$, which is accreting with an Eddington ratio of
$\sim$0.2. We conclude that the analyzed region is consistent with being the
formation site of a secondary BCG. These findings, together with an in-depth
analysis the X-ray morphology of the cluster, suggest a merging scenario of the
entire cluster, with two massive halos both harbouring two rapidly evolving
BCGs on the verge of being assembled. Our results are also consistent with the
scenario in which the AGN phase in member galaxies is triggered by gas-rich
mergers, playing a relevant role in the formation of the red sequence of
elliptical galaxies observed in the center of local galaxy clusters.
