  We report Fermi-LAT observations of the radio-loud AGN SBS 0846+513
(z=0.5835), optically classified as a Narrow-Line Seyfert 1 galaxy, together
with new and archival radio-to-X-ray data. The source was not active at
gamma-ray energies during the first two years of Fermi operation. A significant
increase in activity was observed during 2010 October-2011 August. In
particular a strong gamma-ray flare was observed in 2011 June reaching an
isotropic gamma-ray luminosity (0.1-300 GeV) of 1.0x10^48 erg/s, comparable to
that of the brightest flat spectrum radio quasars, and showing spectral
evolution in gamma rays. An apparent superluminal velocity of (8.2+/-1.5)c in
the jet was inferred from 2011-2012 VLBA images, suggesting the presence of a
highly relativistic jet.
  Both the power released by this object during the flaring activity and the
apparent superluminal velocity are strong indications of the presence of a
relativistic jet as powerful as those of blazars. In addition, variability and
spectral properties in radio and gamma-ray bands indicate blazar-like
behaviour, suggesting that, except for some distinct optical characteristics,
SBS 0846+513 could be considered as a young blazar at the low end of the
blazar's black hole mass distribution.
