  We propose that {\gamma} -rays in blazars can be produced during encounters
of relativistic blobs of plasma with radiation field produced by luminous stars
within (or close to) the jet. The blob is expected to contain relativistic
electrons which comptonize stellar radiation to the GeV-TeV energies. Produced
{\gamma} -rays can initiate the Inverse Compton e+/- pair cascade in the
stellar radiation. We propose that such a scenario can be responsible for the
appearance of the so-called orphan {\gamma} -ray flares. We show that the
relativistic blob/luminous star collision model can explain the appearance of
the extreme orphan {\gamma} -ray flare observed in the GeV and sub-TeV energy
range from the flat spectrum radio quasar PKS 1222+21.
