  We explore the origin of a population of stars recently detected in the inner
parsec of the Milky Way Nuclear Cluster (NC), which exhibit sub-solar
metallicity and a higher rotation compared to the dominant population. Using
state-of-the-art $N$-body simulations, we model the infall of a massive stellar
system into the Galactic center, both of Galactic and extra-galactic origin. We
show that the newly discovered population can either be the remnant of a
massive star cluster formed a few kpc away from the Galactic center (Galactic
scenario) or be accreted from a dwarf galaxy originally located at 10-100 kpc
(extragalactic scenario) and that reached the Galactic center 3-5 Gyr ago. A
comparison between our models and characteristic Galactocentric distance and
metallicity distributions of Milky Way satellites and globular clusters favours
the Galactic scenario. A comparison with clusters associated with the
Enceladus-Sausage, Sequoia, Sagittarius and Canis Major structures suggests
that the progenitor of the observed metal-poor substructure formed in-situ
rather than being accreted.
