The excited teenager shared a snapshot on Twitter of the pair doing the trademark prom photograph pose, complete with a corsage and tropical themed backdrop.
"It's been insane," Peterson dished exclusively to E! News after the memorable night. "I don't want to sleep because it feels surreal."
As for their initial meeting backstage, Peterson said that the "down-to-earth" blond beauty "acted like we had the whole day to kill."
"She didn't rush me at all," he revealed. "She was listening to everything I said and was genuinely blown away by my outfit."
Speaking of his unique ensemble, Peterson donned a custom-made tongue jacket and matching tie for the show.
"My friend and I spent the last week making it ourselves," Peterson shared. "I got photos of Miley's tongue from different shoots and photo shopped them on to iron-on paper. We ironed it on all over, there were a total of 162 tongues on the jacket."
And what did the singing sensation think of his special wardrobe?
"She loved my outfit so much that as soon as I walked in, she ran to grab her cell phone and we took pictures of my outfit and a bunch of selfies on her phone."
The duo planned beforehand that Peterson would join the 21-year-old on stage during her "Adore You" performance.
"She had me on for the entire song, I was just jamming out, pretending like I was in my car," Peterson said.
In the middle of the upbeat tune, Peterson bent down on his knee to present Cyrus with the corsage, and she was quick to make a comment referencing her ex-fiancé Liam Hemsworth.
"I was in this position once before, and it didn't work out too well the last time a guy got on one knee for me," Cyrus said, captured in this YouTube video. "Hopefully this will be better," she quipped.
Jokes about the Hunger Games hunk aside, Peterson couldn't help but gush about his time with Cyrus.
"This whole experience has made me come out of my shell, I was in front of an entire arena and I didn't even care," Peterson said.
He continued: "She was the nicest person. I thought I was in love with her before, she most amazing person."
—Additional reporting by Andrea Martinez