Actress Gwyneth Paltrow, who performed back-up vocals earlier this week, says singing is one of her biggest passions.

The 41-year-old took to the stage with country singer Holly Williams at Los Angeles' legendary Roxy Theatre Monday night and later revealed on Twitter that music comes a close second to acting for her, reports contactmusic.com.

Sharing a picture of the set, she posted on the social networking site: "Singing back-up, my favourite side job @hollywilliams1 @colemantime #latergram".

The actress surprised fans by jumping on the stage with Williams, who was supporting country rocker Jason Isbell, swaying from side-to-side in time with the music.