The singer-turned-actor attended the Marine Corps Ball in Richmond, Virginia on Saturday -- after promising a marine he'd be her date.
Justin was the guest of Corporal Kelsey De Santis -- who invited him to the event in a YouTube video.
De Santis says she decided to invite Justin after he encouraged his "Friends with Benefits" co-star, Mila Kunis, to accept an invitation to the Greenville, North Carolina Marine Corps Ball -- taking place on Nov. 18.
Timberlake talked about the evening on his website -- saying it was "one of the most moving evenings" of his life.
"It hit me all of a sudden that these were the type of people that look after us and our freedom," he says. "Last night changed my life and I will never forget it."
Click through the gallery above to see more photos from the Marine Corps Ball!