  We report the detection of a statistically significant flare-like event in
the Mg II\lambda 2800\AA\ emission line of 3C 454.3 during the outburst of
autumn 2010. The highest levels of emission line flux recorded over the
monitoring period (2008 - 2011) coincide with a superluminal jet component
traversing through the radio core. This finding crucially links the
broad-emission line fluctuations to the non-thermal continuum emission produced
by relativistically moving material in the jet and hence to the presence of
broad-line region clouds surrounding the radio core. If the radio core were
located at several parsecs from the central black hole then our results would
suggest the presence of broad-line region material outside the inner parsec
where the canonical broad-line region is envisaged to be located. We briefly
discuss the implications of broad-emission line material ionized by non-thermal
continuum on the context of virial black hole mass estimates and gamma-ray
production mechanisms.
