  We report on six Chandra and one HST/WFC3 observation of CXO
J122518.6+144545, discovered by Jonker et al. (2010) as a candidate
hyperluminous X-ray source (HLX), X-ray bright supernova or recoiling
supermassive black hole at $L_X = 2.2 \times 10^{41}$ erg/s (if associated with
the galaxy at 182 Mpc). We detect a new outburst of the source in a Chandra
image obtained on Nov 20, 2014 and show that the X-ray count rate varies by a
factor $> 60$. New HST/WFC3 observations obtained in 2014 show that the optical
counterpart is still visible at $g' = 27.1 \pm 0.1$, $1 \pm 0.1$ magnitude
fainter than in the discovery HST/ACS observation from 2003. This optical
variability strongly suggests that the optical and X-ray source are related.
Furthermore, these properties strongly favour an HLX nature of the source over
the alternative scenarios. We therefore conclude that CXO J122518.6+144545 is
most likely an outbursting HLX. It is only the second such object to be
discovered, after HLX-1 in ESO 243-49. Its high X-ray luminosity makes it a
strong candidate to host an intermediate mass black hole.
