Gwyneth Paltrow says singing is her favourite ''side job''.

The 41-year-old actress took to the stage with country singer Holly Williams at Los Angeles' legendary Roxy Theatre on Monday night (28.04.14) and later revealed on Twitter that music comes a close second to acting for her.

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

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

The 'Iron Man 3' star - who has children Apple, nine, and Moses, eight with estranged husband Chris Martin - will no doubt have picked up some tips from the Coldplay frontman, who she split from in March after 10 years of marriage.

The 'Sliding Doors' star has shown off her vocal pipes in the past with a role on hit musical TV show 'Glee', playing Spanish substitute teacher Holly Holliday.

She also starred as an alcoholic Nashville singer in 2010 movie 'Country Strong', a part for which she asked her good pal Beyonce for advice, as well as observing the superstar in action to pick up performance tips.

She explained: ''I watched her [perform] a lot to see how she did it, and I was like 'S**t! I can't do that!'''