And afterwards, he added further insult to injury by winding up Spurs fans on Twitter.
The 24-year-old, who spent five years at Arsenal before leaving for Germany, tweeted: “North London is RED!!!” after the game.
Arsenal let Gnabry leave after an unsuccessful spell on loan at West Brom.
The winger played just ten times for the Gunners, leaving for a lowly £5million in 2016.
Serge Gnabry rubbed salt into the wounds of Spurs fans (Image: GETTY)
Serge Gnabry tweeted 'North London is RED' after the win (Image: GETTY)
But Arsenal fans appeared to have forgotten all about his departure as they celebrated his goals and hilarious tweet.
“Once a gooner always a gooner,” one wrote.
Another posted: “YESSSSSSSSSS SERGE”
“Only Arsenal fans will understand how gassed this makes us,” one joked.
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Serge Gnabry scored four times against Tottenham (Image: GETTY)
“Ending clubs like it’s nothing, you love to see it,” one wrote.
An extremely happy Arsenal fan tweeted: “I LOVE YOU SO MUCH KING”
Tottenham are now third in Group B, two points behind Crvena Zvezda and five behind league leaders Bayern.