Watch: Julia Roberts recalls onstage moment with Taylor Swift, Joan Baez

Dec. 6 (UPI) -- Julia Roberts is looking back on her onstage moment with music superstars Taylor Swift and Joan Baez.

The 56-year-old actress recalled on Tuesday's episode of The Tonight Show starring Jimmy Fallon how she ended up onstage with Swift and Baez at Swift's concert in August 2015.

Roberts and her children, twins Phinnaeus and Hazel and son Henry, were attending Swift's 1989 tour stop in Santa Clara, Calif., when Roberts and Baez joined Swift onstage during her song "Style."

"Taylor had said before the show ... 'Would you like to come on stage?' I was like, 'Oh, I don't know.' I get very nervous," Roberts said.

"And at the time, I think Phin and Hazel were 10 and Henry was 8, and they were like, 'Oh, Mom, you should do it. You should do it.' And Henry goes, 'Don't do it unless you feel comfortable,'" she added.

Roberts asked for a Taylor Swift t-shirt to wear before agreeing to come onstage.

"The whole thing was pretty surreal, and the Joan Baez part of it made it even more surreal," she said.

Swift concluded the first leg of her Eras tour in November and was named Time magazine's Person of the Year on Wednesday.

Roberts will next star in Leave the World Behind, a new film based on the Rumaan Alam novel. Roberts and her co-star Ethan Hawke dazzled at the movie's New York premiere Monday.

Leave the World Behind premieres Friday on Netflix.

On The Tonight Show, Roberts also played a game of Box of Lies with host Jimmy Fallon.