  The formation of galaxies by gradual hierarchical co-assembly of baryons and
cold dark matter halos is a fundamental paradigm underpinning modern
astrophysics and predicts a strong decline in the number of massive galaxies at
early cosmic times. Extremely massive quiescent galaxies (stellar masses
$>10^{11}$ M$_\odot$) have now been observed as early as 1-2 billions years
after the Big Bang; these are extremely constraining on theoretical models as
they form 300-500 Myr earlier and only some models can form massive galaxies
this early. Here we report on the spectroscopic observations with the James
Webb Space Telescope of a massive quiescent galaxy ZF-UDS-7329 at redshift
3.205 $\pm$ 0.005 that eluded deep ground-based spectrscopy, is significantly
redder than typical and whose spectrum reveals features typical of much older
stellar populations. Detailed modelling shows the stellar population formed
around 1.5 billion years earlier in time (z ~ 11) at an epoch when dark matter
halos of sufficient hosting mass have not yet assembled in the standard
scenario. This observation may point to the presence of undetected populations
of early galaxies and the possibility of significant gaps in our understanding
of early stellar populations, galaxy formation and/or the nature of dark
matter.
