  We report on timing observations of the recently discovered binary pulsar PSR
J1952+2630 using the Arecibo Observatory. The mildly recycled 20.7-ms pulsar is
in a 9.4-hr orbit with a massive, M_WD > 0.93 M_sun, white dwarf (WD)
companion. We present, for the first time, a phase-coherent timing solution,
with precise spin, astrometric, and Keplerian orbital parameters. This shows
that the characteristic age of PSR J1952+2630 is 77 Myr, younger by one order
of magnitude than any other recycled pulsar-massive WD system. We derive an
upper limit on the true age of the system of 50 Myr. We investigate the
formation of PSR J1952+2630 using detailed modelling of the mass-transfer
process from a naked helium star on to the neutron star following a
common-envelope phase (Case BB Roche-lobe overflow). From our modelling of the
progenitor system, we constrain the accretion efficiency of the neutron star,
which suggests a value between 100 and 300% of the Eddington accretion limit.
We present numerical models of the chemical structure of a possible
oxygen-neon-magnesium WD companion. Furthermore, we calculate the past and the
future spin evolution of PSR J1952+2630, until the system merges in about 3.4
Gyr due to gravitational wave emission. Although we detect no relativistic
effects in our timing analysis we show that several such effects will become
measurable with continued observations over the next 10 years; thus PSR
J1952+2630 has potential as a testbed for gravitational theories.
