  The majority of long duration ($>2$ s) gamma-ray bursts (GRBs) are believed
to arise from the collapse of massive stars \cite{Hjorth+03}, with a small
proportion created from the merger of compact objects. Most of these systems
are likely formed via standard stellar evolution pathways. However, it has long
been thought that a fraction of GRBs may instead be an outcome of dynamical
interactions in dense environments, channels which could also contribute
significantly to the samples of compact object mergers detected as
gravitational wave sources. Here we report the case of GRB 191019A, a long GRB
(T_90 = 64.4 +/- 4.5 s) which we pinpoint close (<100 pc projected) to the
nucleus of an ancient (>1~Gyr old) host galaxy at z=0.248. The lack of evidence
for star formation and deep limits on any supernova emission make a massive
star origin difficult to reconcile with observations, while the timescales of
the emission rule out a direct interaction with the supermassive black hole in
the nucleus of the galaxy, We suggest that the most likely route for progenitor
formation is via dynamical interactions in the dense nucleus of the host,
consistent with the centres of such galaxies exhibiting interaction rates up to
two orders of magnitude larger than typical field galaxies. The burst
properties could naturally be explained via compact object mergers involving
white dwarfs (WD), neutron stars (NS) or black holes (BH). These may form
dynamically in dense stellar clusters, or originate in a gaseous disc around
the supermassive black hole. Future electromagnetic and gravitational-wave
observations in tandem thus offer a route to probe the dynamical fraction and
the details of dynamical interactions in galactic nuclei and other high density
stellar systems.
