In the video, the trio sang a portion of Mika's 2007 track, "Grace Kelly."
"Duet this if you’re going to be a coach on #TheVoice this fall," Stefani captioned the video.
@gwenstefani#duet with @johnlegendofficial #duet this if you’re going to be a Coach on #TheVoice♬ original sound - Blake Shelton
Stefani first joined The Voice as a coach in 2014 for season 7. She appeared as only a part-time advisor the next season, before stepping into the coach's chair once more for season 9.
Stefani was a part-time advisor again in season 10, missed out on season 11 altogether, and came back as a coach for season 12.
A four-season absence followed, but Stefani did return as a coach for seasons 17 and 19, the latter of which marked her most recent coaching appearance on the show.
Season 19 was also Stefani's first time winning the competition, as her contestant, Carter Rubin, came out victorious.
Stefani missed out on the two most recent seasons of the competition, and will be making her return for season 22 this fall, alongside Shelton and Legend. It's currently unclear who the fourth coach will be.
During her appearances on the show, Stefani fell in love Shelton, a fellow coach. The pair tied the knot in July 2021.