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Julia Roberts has finally spilled on what it was like to dance with Taylor Swift on stage.

On Aug. 15 Swift invited the Oscar-winner and Joan Baez to come out onto the stage during her performance of "Style" at Levi's Stadium in Santa Clara, Calif.

"It was one of those crazy out-of-body moments—I can't tell you anything that happened from the moment I came on stage. "I was so nervous!" Roberts told Extra.

The actress confirmed that the surprise appearance was hardly planned. "I would have washed my hair. I was, like, wearing a ponytail and leggings, tennis shoes ..." the 47-year-old mother of three jokes. "No, she was sweet enough to ask me before the show."

Turns out it was her kids, 8-year-old Henry and 10-year-old twins Phinnaeus and Hazel, who convinced their A-lister mom to hit the stage with the "Blank Space" singer (and 2015 InStyle Social Media Awards nominee—vote for Swift here).

"[Swift] said, 'Would you mind coming onstage during the song and dancing?' And I said to my children, 'What do you think?'"

"'Oh Mom, you have to do it!' " she says they told her. "And my youngest son said, 'Only do it if you want to, Mommy,'" recalls Roberts. "It was so sweet."

Not bad for their first concert!