‘The Voice’ Sneak Peek: Kaylee Shimizu & Elizabeth Evans’ Olivia Rodrigo Cover Is the Best Niall’s Ever Heard

John Legend has a tough decision on his hands on Monday’s all-new episode of The Voice!

Two of the youngest members of Team Legend, Kaylee Shimizu, 17, and Elizabeth Evans, 21, take the stage for their dueling performance in a sneak peek at next week’s Battle Rounds, blowing the coaches away with their cover of Olivia Rodrigo’s “Traitor.”

“That was unbelievable,” Niall Horan marvels. “That was the best version of that song I’ve heard, 100 percent.”

Niall praises Kaylee for having so much talent at such a young age, but tells John that he’s leaning toward Elizabeth to win the Battle. Reba McEntire agrees, noting, “Elizabeth, when you opened your mouth and hit that big note, I was just in awe.”

Gwen Stefani says Kaylee has “one of the most incredible voices I’ve ever heard,” but adds that Elizabeth held her own: “There’s not a lot of girls that have power, and that thing that you have on stage. You’re very original and rare.”

As for their coach, John says the performance was “stunning.”

“Both of you are so interesting and cool,” he raves. “Both of you are ridiculous, I can’t believe I have to make this decision.”

Watch the full audition below and tune in Monday to see who John names as the winner!

ET spoke with Gwen ahead of this season’s Battles, where she opened up about how surreal it is to return to The Voice without hubby Blake Shelton by her side. The Cowboy departed the NBC singing competition earlier this year, after 23 seasons.

“It feels kind of like [my] first season, before I knew he existed,” she shared. “It’s kind of weird, but it’s also like, I’m having so much fun.”

“Like, I’m only here because it’s fun,” Gwen added. “The coaching and actually getting to know your team after the Blinds is my favorite thing, ’cause it’s like, the dream’s there.”

She admitted, however, that it is a little nerve-wracking to look to Blake’s chair and instead see The Voice‘s newest coach — the Queen of Country herself.

Of how Reba’s handled her first season so far, Gwen recalled the Blind Auditions with a laugh.

“She did great. She didn’t have to do anything,” she remembered. “She’d be like, ‘I think you were great. I’d love to have you on my team,’ and then they’d be like, ‘I pick you!'” 

The Voice airs Mondays at 8 p.m. PT and Tuesdays at 9 p.m. PT on NBC.