"I felt so proud to be there," he says. "I felt like I was getting a chance to be among my heroes"

Looks like they had a ball – or, as he tells it, the event “turned out to be one of the most moving evenings I’ve ever had.”

This summer, Justin Timberlake accepted a servicewoman’s invitation to attend the Instructor Battalion Marine Corps Ball, and Saturday he made good on that promise.

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“What I didn’t know was how moved I would be by the whole experience,” Timberlake, 30, posted afterwards on his website.

The singer-actor was combat instructor Kelsey De Santis’s date to Saturday’s dance at the Richmond Convention Center in Richmond, Va.

Of the time the two spent together, Timberlake wrote, “She seemed to me to be so humble and honest… Very cool. She also simultaneously seemed like she was nervous about the whole evening and if I was going to enjoy myself. ‘Are you ok?’ she asked 2 or 3 times. “I hope you are having fun. I know you will once my crew of friends get here to the table.’ ”

He went on to say, “I have to tell you, it’s not every day that I meet a 23 year old girl and she’s more worried about if I’m having fun or if I’m comfortable! It hit me all of a sudden that these were the type of people that look after us and our freedom… Humble, concerned for others before themselves… This was the type of person our Marine Corps was building. I was really blown away.”

Timberlake had been wooed to the ball via video, when his Marine, a champion mixed martial artist in her off-time, made her plea on YouTube. “So, Justin,” she said in her online invite. “I’m going to call you out and ask you to come to the Marine Corps ball with me on Nov. 12. … And if you can’t go, all I have to say is, cry me a river.”

Luckily, she had nothing to cry about.

One fellow Marine who attended the ball told PEOPLE, “We all brought sexy back! Justin seemed to have a good time, and it was great to see him there.”