  AT 2021loi is an optical-ultraviolet transient located at the center of its
host galaxy. Its spectral features identify it as a member of the ``Bowen
Fluorescence Flare'' (BFF) class. The first member of this class was considered
to be related to a tidal disruption event, but enhanced accretion onto an
already active supermassive black hole was suggested as an alternative
explanation. AT 2021loi, having occurred in a previously-known unobscured AGN,
strengthens the latter interpretation. Its light curve is similar to those of
previous BFFs, showing a rebrightening approximately one year after the main
peak (which was not explicitly identified, but might be the case, in all
previous BFFs). An emission feature around 4680 A, seen in the pre-flare
spectrum, strengthens by a factor of $\sim$2 around the optical peak of the
flare, and is clearly seen as a double peaked feature then, suggesting a blend
of NIII $\lambda 4640$ with HeII $\lambda4686$ as its origin. The appearance of
OIII $\lambda$3133 and possible NIII $\lambda\lambda4097,4103$ (blended with
H$\delta$) during the flare further support a Bowen Fluorescence
classification. Here, we present ZTF, ATLAS, Keck, Las Cumbres Observatory,
NEOWISE-R, $Swift$, AMI and VLA observations of AT 2021loi, making it one of
the best observed BFFs to date. AT 2021loi thus provides some clarity on the
nature of BFFs but also further demonstrates the diversity of nuclear
transients.
