Indio, California - Olivia Rodrigo proved she's a fangirl at heart with a viral new TikTok starring herself and No Doubt's Gwen Stefani.

After making a surprise appearance during No Doubt's Coachella performance on Saturday, the 21-year-old singer gave fans a peek behind the curtain with a video from rehearsals.

In the clip shared Sunday, Gwen lip-synced to an audio of herself doing a call-and-response during the band's hit song, Just A Girl.

While the sound features a heavy crowd, Liv took duties into her own hands, filling the barricaded pit all by her lonesome, singing and jumping in reply to Gwen.

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"im the biggest no doubt fangirl," Olivia wrote in TikTok's caption. "was such an honor to sing with them at @coachella last night!!! ily @Gwen Stefani !!!!"

The Grammy winner sang Bathwater with No Doubt during her unannounced Coachella performance, and she later revealed via Instagram that the track holds a special meaning to her.

"I remember hearing bathwater for the first time when I had just started writing songs," Olivia wrote. "it totally turned my world on its head and inspires me to this day."

She added that it was the "coolest honor" to join the band for the show and called them "out of the world."

The get him back! artist played on her GUTS World Tour encore outfit for her Coachella look, rocking a white "I heart ND" tank over a red bra.

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She paired the top with black pants and a studded "ND" belt.

Olivia recently showed her love for another '90s hit, Jewel's You Were Meant for Me, at her final show at Madison Square Garden, which featured a surprise appearance by the 49-year-old singer-songwriter herself!