In 2014, an anomalous 3.5 keV line was observed in the spectra of galaxy clusters by Bulbul et al and Boyarsky et al. Numerous explanations of this feature, both dark matter based and astrophysical, have been proposed. I will review the observational status of the 3.5 keV line and its potential as a dark matter signal. I will also discuss our recent discovery of an absorption feature at 3.5 keV in the AGN at the centre of the Perseus galaxy cluster, and how these anomalies may be linked. In particular, our result means that the non-observation of the 3.5 keV line with Hitomi is fully consistent, and could be explained in a two-state Fluorescent Dark Matter model for the 3.5 keV line.
