  We report results of a multiband monitoring campaign of the flat spectrum
radio quasar TXS 0536+145 at redshift 2.69. This source was detected during a
very high gamma-ray activity state in 2012 March by the Large Area Telescope on
board Fermi, becoming the gamma-ray flaring blazar at the highest redshift
detected so far. At the peak of the flare the source reached an apparent
isotropic gamma-ray luminosity of 6.6 x 10^49 erg/s which is comparable to the
values achieved by the most luminous blazars. This activity triggered
radio-to-X-rays monitoring observations by Swift, Very Long Baseline Array,
European VLBI Network, and Medicina single-dish telescope. Significant
variability was observed from radio to X-rays supporting the identification of
the gamma-ray source with TXS 0536+145. Both the radio and gamma-ray light
curves show a similar behaviour, with the gamma-rays leading the radio
variability with a time lag of about 4-6 months. The luminosity increase is
associated with a flattening of the radio spectrum. No new superluminal
component associated with the flare was detected in high resolution
parsec-scale radio images. During the flare the gamma-ray spectrum seems to
deviate from a power law, showing a curvature that was not present during the
average activity state. The gamma-ray properties of TXS 0536+145 are consistent
with those shown by the high-redshift gamma-ray blazar population.
