Maggie Diaz arrived at Wyandanch Memorial High School's prom on Friday at the Crest Hollow Country Club in Woodbury without a date.

That didn't last long.

She was taken by surprise when her boyfriend, Justyn Sanabria, clad in his Army dress uniform, popped up to greet her.

"It meant everything," Diaz, 18, said. "I didn't expect him to come. I was in shock."

Sanabria's decision to attend his girlfriend's prom was made on a whim.

"I knew just today," he said at the prom. "It was 12 o'clock and I told myself, 'I'm going. I'm going.' I got here an hour or two ago." Sanabria will return to Fort Drum, an Army installation in upstate, on Monday.

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Diaz said Sanabria's drive from Fort Drum takes six hours. Sanabria had told her not to show up early to prom because he planned to have someone deliver her flowers. But, it was really so he could get there in time to surprise her.

Eighty-seven students attended the Wyandanch prom. Friends and faculty surrounded the couple to take photos and capture the moment.

"I started to cry," said class adviser Kris Baker. "I know their story and I was so happy he came for her. It warmed my heart."

Sanabria left for Army basic training on Oct. 6, 2014. He and Diaz met more than three years ago at Wyandanch's Military Ball, an event hosted by the school's JROTC (Junior Reserve Officer Training Corps) program.

"I went to take a picture with my friend, but I couldn't find her," Diaz said. "He went and took a picture with me. I didn't know him. After that, we sat together for dinner. And we've been talking ever since."