  The survey of galaxy clusters performed by Planck through the
Sunyaev-Zeldovich effect has already discovered many interesting objects,
thanks to the whole coverage of the sky. One of the SZ candidates detected in
the early months of the mission near to the signal to noise threshold,
PLCKG214.6+37.0, was later revealed by XMM-Newton to be a triple system of
galaxy clusters. We have further investigated this puzzling system with a
multi-wavelength approach and we present here the results from a deep
XMM-Newton re-observation. The characterisation of the physical properties of
the three components has allowed us to build a template model to extract the
total SZ signal of this system with Planck data. We partly reconciled the
discrepancy between the expected SZ signal from X-rays and the observed one,
which are now consistent at less than 1.2 sigma. We measured the redshift of
the three components with the iron lines in the X-ray spectrum, and confirmed
that the three clumps are likely part of the same supercluster structure. The
analysis of the dynamical state of the three components, as well as the absence
of detectable excess X-ray emission, suggest that we are witnessing the
formation of a massive cluster at an early phase of interaction.
