Hennigan, 16, sang Jewel's "Foolish Games" during this season's final blind auditions episode. It took awhile for any of the coaches to hit their buttons, but eventually Shelton did and was blown away by the performance.
Right after she finished singing, the other coaches regretted not hitting their buttons.
"You gotta be kidding me!" Shelton said to the other coaches as he walked up to hug Hennigan. "What in the hell just happened?"
"I think you're awesome and I have nothing to say for myself, but I'm ashamed," Adam Levine said.
"Your voice is developed well beyond your years," John Legend added. "The main thing for you is showcasing that powerful instrument you have and you'll do great on the show."
Shelton told her they will have to find songs she can "blow the roof off this place" with.
Hennigan became a viral superstar in August 2018 after she shared a video of herself singing a perfect rendition of Todrick Hall's "McDonald's Drive-Thru Song." She shared the original video on Facebook, where it has over 2.3 million views, more than 2,700 comments and over 37,900 shares.
"I just loved it when I was a kid," Hennigan told The Today Show last summer. "I just happened to memorize the words and when I was at McDonald's the other night, it just kind of happened. It was a spur-of-the-moment thing."
Hennigan tried out for The Voice during auditions in Atlanta. However, the special moment almost did not happen.
"The whole day was crazy," Hennigan told MyHorryNews.com. "There were some complications getting me into the audition because I am a minor and could only bring one adult with me, and my little sister was with us. I was worried they were going to tell me I couldn't audition. People were so kind, though."
Hennigan said she needed to perform a song for a casting producer before she could sing for Shelton, Legend, Levine and Kelly Clarkson. She performed "Gravity" by Sara Bareilles, which impressed the producer.
Hennigan performed "Foolish Games" and Rachel Platten's "Fight Song" for the producer before getting a second callback to sing for the coaches.
New episodes of The Voice air Mondays on NBC at 8 p.m. ET.
Photo credit: Instagram/Cecily Hennigan