  QSO B0218+357 is a blazar located at a cosmological redshift of z=0.944. It
is gravitationally lensed by a spiral galaxy at a redshift of z=0.68. The
blazar and its lens are well studied in the radio through X-ray bands, and
several blazar outbursts were detected by Fermi-LAT at energies above 100 MeV.
Strong gravitational lensing was invoked to explain the two components appar-
ent in the radio and GeV light curves, separated by 10-12 days. In July 2014
another outburst was observed by Fermi-LAT, triggering follow-up observations
with the MAGIC telescopes at energies above 100 GeV. The observations were
scheduled at the expected time of arrival of the component delayed by the
strong gravitational field of the lens, resulting in a firm detection of QSO
B0218+357. Using the combined Fermi-LAT and MAGIC data sets, we report on
variability of this unique blazar, the most distant among all currently known
very high energy sources.
