  Finding the first generation of stars formed out of pristine gas in the early
Universe, known as Population III (PopIII) stars, is one of the most important
goals of modern astrophysics. Recent models have suggested that PopIII stars
may form in pockets of pristine gas in the halo of more evolved galaxies. We
present NIRSpec integral field spectroscopy and micro-shutter array
spectroscopic observations of the region around GN-z11, an exceptionally
luminous galaxy at z=10.6, that reveal a greater than 5 sigma detection of a
feature consistent with being HeII1640 emission at the redshift of GN-z11. The
very high equivalent width of the putative HeII emission in this clump
(log(EW_rest(HeII)/A) = 1.79) and a lack of metal lines can be explained in
terms of photoionisation by PopIII stars, while photoionisation by PopII stars
is inconsistent with the data. The high equivalent width would also indicate
that the putative PopIII stars likely have an initial mass function with an
upper cutoff reaching at least 500 Msun. The PopIII bolometric luminosity
inferred from the HeII line would be 7 x 10^9 Lsun, which would imply a total
stellar mass formed in the burst of about 2 x 10^5 Msun. We find that
photoionisation by the active galactic nucleus (AGN) in GN-z11 cannot account
for the HeII luminosity observed in the clump but can potentially be
responsible for an additional HeII emission observed closer to GN-z11. We also
consider the possibility of in situ photoionisation by an accreting direct
collapse black hole hosted by the HeII clump. We find that this scenario is
less favoured, but it remains a possible alternative interpretation. We also
report the detection of a Ly-alpha halo stemming out of GN-z11 and extending
out to about 2 kpc as well as resolved funnel-shaped CIII emission likely
tracing the ionisation cone of the AGN.
