  We report on the discovery of the companion star to the millisecond pulsar
PSR J1835-3259B in the Galactic globular cluster NGC 6652. Taking advantage of
deep photometric archival observations acquired through the Hubble Space
Telescope in near-ultraviolet and optical bands, we identified a bright and
blue object at a position compatible with that of the radio pulsar. The
companion is located along the helium-core white dwarf cooling sequence and the
comparison with binary evolution models provides a mass of $0.17 \pm
0.02~M_\odot$, a surface temperature of $11500\pm1900$ K and a very young
cooling age of only $200\pm100$ Myr. The mass and the age of the companion are
compatible with a progenitor star of about $0.87~M_{\odot}$, which started
transferring mass to the primary during its evolution along the sub-giant
branch and stopped during the early red giant branch phase. Combining together
the pulsar mass function and the companion mass, we found that this system is
observed at an almost edge-on orbit and hosts a neutron star with a mass of
$1.44 \pm 0.06~M_\odot$, thus suggesting a highly non-conservative mass
accretion phase. The young age of the WD companion is consistent with the
scenario of a powerful, relatively young MSP indicated by the earlier detection
of gamma-rays from this system.
