The ad, which dates to 2008, shows a fry made to look like a raised middle finger, Mashable reports.
The image is being shared widely on social media after two separate explosions Tuesday morning at Brussels-Zaventem Airport and Maelbeek metro station, which killed more than 30 people and injured hundreds.
ISIS has claimed responsibility for the attacks, according to the Amaq Agency which is known to be affiliated with the terrorist group.
Fries are a national symbol in Belgium, which is likely why the Burger King ad has resurfaced and gained traction online since the attacks.
Here is the ad: