  Small kinematically-decoupled stellar discs with scalelengths of a few tens
of parsec are known to reside in the centre of galaxies. Different mechanisms
have been proposed to explain how they form, including gas dissipation and
merging of globular clusters. Using archival Hubble Space Telescope imaging and
ground-based integral-field spectroscopy, we investigated the structure and
stellar populations of the nuclear stellar disc hosted in the interacting SB0
galaxy NGC 1023. The stars of the nuclear disc are remarkably younger and more
metal rich with respect to the host bulge. These findings support a scenario in
which the nuclear disc is the end result of star formation in metal enriched
gas piled up in the galaxy centre. The gas can be of either internal or
external origin, i.e. from either the main disc of NGC 1023 or the nearby
satellite galaxy NGC 1023A. The dissipationless formation of the nuclear disc
from already formed stars, through the migration and accretion of star clusters
into the galactic centre is rejected.
