Kelly Clarkson and Brett Eldredge just came out with a holiday duet called "Under the Mistletoe."They performed it during the live shows on The Voice.It was certainly hard for fans to miss their undeniable chemistry.Kelly and Brett worked together on the holiday song that they first performed on NBC's "Christmas in Rockefeller Center." Kelly smiled throughout the entire performance. The pair did maintain their social distance on stage amid the coronavirus pandemic. The music stars then took the song to The Voice stage. Kelly wore a gorgeous red gown as they belted the tune. "They spent lots of time together in the studio and on the phone, and really bonded while they were cutting this sexy song," a source told Us Weekly. They added that "there was some flirting going on.""Kelly's swooning over Brett's handsome face and gentlemanly manners" the source continued. "On the one hand, it's just what she needs for her confidence but there's genuine concern because Brett's a real lady-killer who could leave her brokenhearted."