  The first (Pop III) stars formed only out of H and He and were likely more
massive than present-day stars. Massive Pop III stars in the range 140-260
M$_\odot$ are predicted to end their lives as pair-instability supernovae
(PISNe), enriching the environment with a unique abundance pattern, with high
ratios of odd to even elements. Recently, the most promising candidate for a
pure descendant of a zero-metallicity massive PISN (260 M$_{\odot}$) was
discovered by the LAMOST survey, the star J1010+2358. However, the key elements
to verify the high PISN contribution, C and Al, were missing from the analysis.
To rectify this, we obtained and analyzed a high-resolution VLT/UVES spectrum,
correcting for 3D and/or non-LTE effects. Our measurements of both C and Al
give much higher values (~1 dex) than expected from a 260 M$_{\odot}$ PISN.
Furthermore, we find significant discrepancies with the previous analysis, and
therefore a much less pronounced odd-even pattern. Thus, we show that
J1010+2358 cannot be a pure descendant of a 260 M$_{\odot}$ PISN. Instead, we
find that the best fit model consists of a 13 M$_{\odot}$ Pop II core-collapse
supernova combined with a Pop III supernova. Alternative, less favoured
solutions $(\chi^2/\chi^2_{\rm best}\approx2.3)$ include a 50% contribution
from a 260 M$_{\odot}$ PISN, or a 40% contribution from a Pop III type Ia
supernova. Ultimately, J1010+2358 is certainly a unique star giving insights
into the earliest chemical enrichment, however, this star is not a pure PISN
descendant.
