The Oscar winner, 45, and the Coldplay frontman, 40, performed at their son Moses' school fundraiser parent talent show on Saturday, February 24 at the swanky Roosevelt Hotel in Hollywood.
"Gwyneth opened the show on stage singing "Despacito" by Justin Bieber by herself, and the crowd went wild," a witness dished to Radar.
Wearing a black pants suit with a long sleeved black sweater and her hair in pig tails, Paltrow also sported her giant diamond ring on her left hand. (The pair is engaged to longtime boyfriend Brad Falchuk, 46.)
After her debut, Martin joined her on stage.
"Chris came up and they sang 'Bombeleo,'" the source told Radar about the Gipsy Kings tune. "Then they sang another Cuban song together."
"Gwyneth and Chris were so friendly with each other and the other parents, it was a great night," the insider added.
The Country Strong actress sang all of the songs in that movie when she played a struggling country singer.
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