'The Voice': 4-Chair Turn Aaron Hines Harmonizes With John Legend -- But Makes a Surprising Choice!

Aaron harmonized with John Legend on 'All of Me,' but did he choose Team Legend?

The coaches' teams are almost full on season 21 of The Voice -- but when a singer like Aaron Hines takes the stage, everyone has to hit their button!

On Tuesday, the San Antonio, Texas, native took the stage to impress the coaches with his cover of Giveon's "Heartbreak Anniversary," earning one of the season's last four-chair turns.

John Legend was the first to hit his button, and was quick to tell Aaron, "I love your voice."

"You just sounded like you knew what you wanted to do with the song," he added. "You went out there and executed it beautifully."

Aaron thanked John for his praise, adding, "I can't tell you how many times I've sang 'All of Me' at weddings."

The EGOT winner then prompted Aaron to sing a bit of his 2013 smash hit single, and the two harmonized on the iconic chorus.

"I'm feeling very confident," Kelly Clarkson joked after the moving moment, though Aaron insisted: "I promise, I love you too!"

Blake Shelton tried to use the awesome duet against John later, when he made the case for himself over his fellow coaches. 

"[John] always has his artists sing his songs, because he gets paid," Blake teased. "Congratulations, you made a little extra money today."

Ultimately, Aaron borrowed one of John's favorite phrases and "shocked the world" by choosing to join Team Kelly!

"I feel like she got me, artistically," Aaron told host Carson Daly backstage of his surprising choice.

"I was so shocked he picked me!" Kelly admitted, raving about her new team member and his vocal range. "But, he's San Antonio, Texas, so, what up?"

With just one night of Blind Auditions remaining, check out ET's complete roundup of the season 21 team rosters and follow along with your favorites.

Ahead of season 21, John Kelly and Blake placed a target on Ariana Grande's back as the first-time coach this season -- especially because so many of the show's young singers idolize the two-time GRAMMY winner's vocal talent and chart success.

"Of course she's a threat!" John said with a laugh during their preseason press conference. "She is hugely talented, hugely successful and has legions and legions of fans that know how to use the internet and vote."

"There's no disadvantage when you're Ariana Grande," Kelly agreed. "She can't say it. I will."

"It's embarrassing to follow her [onto the Voice stage]," Blake joked of the audience's enthusiasm for the "7 Rings" singer. "It exposes my lack of celebrity."

As a longtime "huge fan of The Voice," Ariana was humble about her possible advantages, but said she couldn't wait for fans to see how her season 21 team comes together.

"I have watched many seasons and I love watching the show," she said. "It always has the best energy. It's such wholesome, inspiring television, and I love seeing the different voices and watching so many people start careers for themselves. It's a beautiful, amazing thing."

The Voice airs Mondays and Tuesdays at 8 p.m. PT/ET on NBC. See more from this season in the video below.