Watch Taylor Swift bring out Little Mix, Joan Baez and Julia Roberts at 1989 concert

Julia Roberts Joins Taylor Swift on Stage

Taylor Swift celebrated girl power at her back-to-back concerts at Levi's Stadium in Santa Clara, Calif., over the weekend.

Watch Taylor Swift and Fifth Harmony Perform 'Worth It' at Levi's Stadium

On Friday night (Aug. 14), Swift invited Fifth Harmony. on stage to perform their hit song "Worth It," and the following evening she brought out Little Mix to play their new single "Black Magic."

The massive stadium crowd loved it. "LITTLE MIX!! Love these girls!! They smashed it tonight in front of 50,000 screaming fans. Amazing," Swift tweeted after the show.

Taylor Swift's On-Stage Guests See Increased Hype, Says Data

Little Mix, meanwhile, was left in disbelief after the performance. "OMG cannot quite believe what's just happened, one of the best experiences in our little mix life ever!" the British act posted on Instagram.

"Black Magic," from Little Mix's upcoming third album Get Weird, recently became the pop outfit's longest-running U.K. No. 1 single. The group is slated to perform at the Billboard Hot 100 Music Festival, to be held Aug. 22-23 at New York's Jones Beach.

Little Mix wasn't the only surprise guest on Saturday. Swift also invited legends Joan Baez and Julia Roberts to the stage during "Style." The beloved folk singer and Oscar-winning actress "danced it out to 'Style,'" Swift tweeted. "These two women are my heroes. What an honor."

Other surprise guests on Swift's ongoing 1989 tour have included Fetty Wap, Nick Jonas, The Weeknd and Lorde.

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