  We report a dramatic variability event in the X-ray history of the
Narrow-Line quasar PHL 1092 (z=0.396). Our latest 2008 XMM-Newton observation
reveals a flux drop of ~200 with respect to the previous observation performed
about 4.5 years earlier, and a drop of ~135 with respect to its historical
flux. Despite the huge X-ray variation, the UV flux remains constant producing
a very significant steepening of the optical to X-ray slope alpha_ox from -1.56
to -2.44, making PHL 1092 one of the most extreme X-ray weak quasars. The
similarity in the soft X-ray spectral shape between the present and previous
observations, together with the persistent UV flux and the lack of any dramatic
change in the optical spectrum suggest that an absorption event is not likely
to be the origin of the observed variation. If absorption is ruled out, the
sudden X-ray weakness of PHL 1092 must be produced by a transient significant
weakening or disruption of the X-ray emitting corona.
