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

AT 2021loi: A Bowen Fluorescence Flare with a Rebrightening Episode, Occurring in a Previously-Known AGN