Gnabry scored a hat-trick on his debut for Germany against San Marino away from home in 2018 FIFA World Cup qualification UEFA Group C.
The 21-year-old found the net in the ninth, the 58th and the 76th minute of the encounter at the San Marino Stadium.
Spain international right-back Bellerin has congratulated his former Arsenal teammate Gnabry on his heroics on Twitter.
The youngster left the Gunners for German club Werder Bremen in the summer transfer window.
Bremen have trolled Arsenal on Twitter following Gnabry’s heroics for the Germany national team.
Gnabry has scored four goals and created 18 chances in nine Bundesliga appearances for Bremen so far this season.
Alexander Nouri’s side are third from bottom in the league table at the moment with just seven points from 10 matches.
Meanwhile, Arsenal are currently fourth in the Premier League table with 24 points from 11 games, just two points behind leaders Liverpool.