It’s official: Gwen Stefani and Blake Shelton have musical chemistry on top of romantic chemistry.

The couple took to The Voice stage on Monday’s episode to perform their duet “Go Ahead and Break My Heart” for the first time on air.

Stefani, 46, looked beautiful in a sheer, mermaid-style Jaime Lee gown which featured sparkling jewels throughout her dress while Shelton, 39, looked dapper in a white dress shirt, black vest, color coordinated pants and tie.

After the performance, the country star exclusively opened up to PEOPLE about his collaboration with his girlfriend. “I guess I’m nervous in a new kind of way,” he said. “I’m excited because this is a song Gwen and I feel so close to for obvious reasons. It’s as brutally honest and straightforward as you can be in a love song.”

If Shelton had nerves when he took the stage, fans and viewers couldn’t notice because all eyes were on the couple’s stage presence. “When they were introduced to the stage, Blake gently touched her lower back, helping her up the stairs,” an onlooker tells PEOPLE.

And that was only the beginning of their PDA-packed performance, which took two takes to film.

“The moment he saw her, he couldn’t help but smile,” the eyewitness says about the first run. “The two shared plenty of sweet, intimate moments during their performance, barely breaking eye contact. When it came to singing, you could tell they were very much in the moment. Once the song finished, Blake embraced Gwen with a hug and a long kiss on the forehead.”

Although the second take was “very similar” to the first, there was no forehead kiss at the end, just a hug. And unfortunately for viewers at home, the second take was the one that aired on NBC.

Before the show, Shelton opened up to PEOPLE about the “serious insecurities” he had over performing the duet.