  In this paper we propose a new plausible mechanism of supernova explosions
specific to close binary systems. The starting point is the common envelope
phase in the evolution of a binary consisting of a red super giant and a
neutron star. As the neutron star spirals towards the center of its companion
it spins up via disk accretion. Depending on the specific angular momentum of
gas captured by the neutron star via the Bondi-Hoyle mechanism, it may reach
millisecond periods either when it is still inside the common envelope or after
it has merged with the companion core. The high accretion rate may result in
strong differential rotation of the neutron star and generation of the
magnetar-strength magnetic field. The magnetar wind can blow away the common
envelope if its magnetic field is as strong as $10^{15}\,$G, and can destroy
the entire companion if it is as strong as $10^{16}\,$G. The total explosion
energy can be comparable to the rotational energy of a millisecond pulsar and
reach $10^{52}\,$erg. However, only a small amount of $^{56}$Ni is expected to
be produced this way. The result is an unusual type-II supernova with very high
luminosity during the plateau phase, followed by a sharp drop in brightness and
a steep light-curve tail. The remnant is either a solitary magnetar or a close
binary involving a Wolf-Rayet star and a magnetar. When this Wolf-Rayet star
explodes this will be a third supernovae explosion in the same binary.
