  By using XSHOOTER spectra acquired at the ESO Very Large Telescope, we have
studied the surface chemical composition of the companion star to the binary
millisecond pulsar PSR J1740-5340 in the globular cluster NGC 6397. The
measured abundances of Fe, Mg, Al and Na confirm that the star belongs to the
cluster. On the other hand, the measured surface abundance of nitrogen
([N/Fe]=+0.53 +- 0.15 dex) combined with the carbon upper limit ([C/Fe] <-2
dex) previously obtained from UVES spectra allow us to put severe constraints
on its nature, strongly suggesting that the pulsar companion is a deeply peeled
star. In fact, the comparison with theoretical stellar models indicates that
the matter currently observed at the surface of this star has been processed by
the hydrogen-burning CN-cycle at equilibrium. In turn, this evidence suggests
that the pulsar companion is a low mass (~0.2 Msun) remnant star, descending
from a ~0.8 Msun progenitor which lost ~70-80 % of its original material
because of mass transfer activity onto the pulsar.
