  Nuclear star clusters (NSCs) are massive star clusters found in the innermost
region of most galaxies. While recent studies suggest that low-mass NSCs in
dwarf galaxies form largely out of the merger of globular clusters and NSCs in
massive galaxies accumulate mass primarily through central star formation, the
formation channel of the Milky Way's NSC is still uncertain. In this work, we
use GigaEris, a high resolution N-body, hydrodynamical, cosmological
``zoom-in'' simulation, to investigate a possible formation path of the NSC in
the progenitor of a Milky Way-sized galaxy, as well as its relation to the
assembly and evolution of the galactic nuclear region. We study the possibility
that bound, young, gas-rich, stellar clusters within a radius of 1.5 kpc of the
main galaxy's centre at z>4 are the predecessors of the old, metal-poor stellar
population of the Milky Way's NSC. We identify 47 systems which satisfy our
criteria, with a total stellar mass of $10^{7.5}$ M$_{\odot}$. We demonstrate
that both stellar cluster accretion and in-situ star formation will contribute
to the formation of the NSC, providing evidence for a hybrid formation scenario
for the first time in an N-body, hydrodynamical, cosmological ``zoom-in''
simulation. Additionally, we find that the gas required for in-situ star
formation can originate from two pathways: gas-rich stellar clusters and gas
influx driven by large-scale non-axisymmetric structures within the galaxy.
This is partly supported by the presence of a stellar ring, resulting from gas
dynamics, with properties similar to those of the Milky Way's nuclear stellar
disc.
