“Hurricane Katrina touched our customers, communities we serve, and our associates in a profound way,” McMillon said in the video posted on the photo-sharing network, which received 132 “likes” in its first five hours.

The catastrophic storm made landfall on Aug. 29, 2005, ravaging New Orleans in what U.S. officials have called the most devastating natural disaster in the nation’s history.

“We haven’t forgotten,” McMillon said in a separate statement released by Walmart. The retail giant, together with its charitable arm Walmart Foundation, will dole out the $25 million gift over five years to organizations specializing in disaster recovery and relief. “We will continue to help communities prepare for—and recover from—the unexpected,” McMillon continued.

See McMillon’s Instagram post announcing the gift here:

New Orleans mayor Mitch Landrieu also recognized Walmart’s own work to help the city recover from the storm, saying it “opened make-shift stores,” sent “truckloads of supplies,” and “activated associates on the ground to help,” according to the company’s official announcement. “When Hurricane Katrina struck the Gulf Coast, Walmart was on the front lines of the response,” Landrieu said. “In turn, they started to change the role of the private sector in disaster response.”

McMillon’s decision to use Instagram to announce the philanthropic gift reflects his growing closeness to the social media company, which is owned by Facebook (FB). Last September, Instagram co-founder Kevin Systrom joined Walmart’s board, and McMillon began posting photos to his personal Instagram account in June.

For more on McMillon and his leadership style, see Fortune’s profile of “The man who’s reinventing Walmart,” from the recent June 15 issue of the magazine.