  Recently, a new class of white dwarfs (``slowly cooling WDs'') has been
identified in the globular cluster M13. The cooling time of these stars is
increased by stable thermonuclear hydrogen burning in their residual envelope.
These WDs are thought to be originated by horizontal branch (HB) stars
populating the HB blue tail, which skipped the asymptotic giant branch phase.
To further explore this phenomenon, we took advantage of deep photometric data
acquired with the Hubble Space Telescope in the near-ultraviolet and
investigate the bright portion of the WD cooling sequence in NGC 6752, another
Galactic globular cluster with metallicity, age and HB morphology similar to
M13. The normalized WD luminosity function derived in NGC 6752 turns out to be
impressively similar to that observed in M13, in agreement with the fact that
the stellar mass distribution along the HB of these two systems is almost
identical. As in the case of M13, the comparison with theoretical predictions
is consistent with $\sim 70\%$ of the investigated WDs evolving at slower rates
than standard, purely cooling WDs. Thanks to its relatively short distance from
Earth, NGC 6752 photometry reaches a luminosity one order of a magnitude
fainter than the case of M13, allowing us to sample a regime where the cooling
time delay, with respect to standard WD models, reaches $\sim 300$ Myr. The
results presented in this paper provide new evidence for the existence of
slowly cooling WDs and further support to the scenario proposing a direct
causal connection between this phenomenon and the horizontal branch morphology
of the host stellar cluster.
