Blake Shelton and Christina Aguilera are co-workers, serving as coaches on 'The Voice.' But they also duet on 'Just a Fool,' a torchy ballad from her new album 'Lotus.' They performed an emotional, gripping and ultimately moving rendition of the song on 'The Ellen Show' yesterday (Dec. 7) and if we didn't know any better, we'd think there was something between the singers!

Relax, we're speaking about their vocal chemistry. Their significant others - Miranda Lambert and Matt Rutler, respectively- have nothing to worry about, as Shelton and Aguilera were entertainers doing their thing to the hilt. They captured the element of longing, loss and pining for someone who is bad for you in their vocal delivery and how they face each other on stage.

They sang the entire song facing one another, and looking at each other intently, making the lyrics and the emotion totally believable.

Xtina started the song out on the stage, backed only by her band. Shelton walked on the stage when it was time to sing his first part, which was a cool way to introduce him into the song and to the crowd.

'Just a Fool' is a terrific, classic duet. It sounds even better when done live.

Last week, Aguilera went on record to say that Shelton has the strongest team left on the show. Her final contestant was eliminated, so she is merely a spectator at this point, supporting her duet partner!