We report the detection of a transient \gamma -ray source in the direction of B3 1428+422 ( z = 4.72 ) by analyzing the 110-month Fermi -LAT Pass 8 data .
The new transient \gamma - ray source is far away from the Galactic plane and has a rather soft spectrum , in agreement with being a high redshift blazar .
We suggest that the newly discovered transient is the \gamma -ray counterpart of B3 1428+422 , which could be the most distant GeV source detected so far .
The detection of a group of such distant \gamma - ray blazars will be helpful to reconstruct the evolution of the luminosity function and to study the extragalactic background light at such high redshifts .