May 20, 2018 03:15 PM

Julia Roberts is rarely seen on social media, but that doesn’t mean she hasn’t mastered the art of the selfie.

The 50-year-old actress — who told Marie Claire in 2013 that she thinks of social media like “appealing” yet “sticky” cotton candy — made an appearance on plenty of Instagram pages on Saturday after attending Taylor Swift‘s show at the Rose Bowl in Pasadena, California. She decided to document the night with some celebrity pals also in attendance, like Rebel Wilson and Amber Rose, pictures of whom Entertainment Tonight host Carly Steel shared on the social media app.

“Amber really wanted a photo with Julia and all the stars in the room and organized it grabbing Rebel and Carly and corralling everyone into it. And then afterwards Julia wanted one too,” a source tells PEOPLE of how the star-studded selfie, taken by Roberts, came to be.

Carly Steel/Instagram
Julia Roberts, Rebel Wilson and Amber Rose
Rebel Wilson/Instagram

Swift, 28, also joined in on the fun, as evidenced by backstage photos shared by Wilson, 38.

“The concert was so star packed. The green room was crazy,” the insider adds. “Taylor came in to do a meet and greet and chatted to everyone. It was basically just celebrities and their kids.”

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The stars also had a blast during the concert, sharing videos of the performance on their pages.

“They were all dancing in the VIP box having an amazing time,” the source says.

Rebel Wilson and Carly Steel
Carly Steel/Instagram
Carly Steel and Rebel Wilson
Carly Steel/Instagram
Amber Rose's son, Sebastian
Amber Rose/Instagram

Rose, 34, brought ex Wiz Khalifa, 30, and their son Sebastian, who knew every word to the songs and sang along throughout the show. The insider says Sebastian, 5, even gave Swift a bouquet, adding that the two women became close after Rose was supportive of her through her feud with Kanye West, Rose’s ex.

Other celebrities at the concert included Lena Dunham, Bill Nye, Kobe Bryant, Sarah Michelle Gellar and her kids and Miles Teller and his fiancée Keleigh Sperry.

Bill Nye
Taylor Swift/Instagram

There was another celebrity sighting, but this one was onstage: Selena Gomez surprised the crowd to sing her hit “Hands to Myself.”

Sharing a behind the scenes look at their rehearsal process on her Instagram Story, Swift and her longtime BFF laughed with each other as they prepared for the big day.

“We’re gonna sing ‘Hands to Myself’ which is a[n] absolutely iconic bop,” Swift said, while sharing a sweet moment with Gomez, 25, ahead of the show.

“Yes, Taylor loves that one, and I love her for loving it,” Gomez replied.

“It’s my favorite song,” Swift insisted.

Taylor Swift and Selena Gomez
Christopher Polk/TAS18/Getty Images
Selena Gomez and Taylor Swift
Taylor Swift/Instagram

After sharing a clip of their energetic performance together, Swift wrote a sweet note to her friend on social media.

“To the person I could call at any time of day, who has been there no matter what… you absolutely KILLED IT tonight and everyone was so excited to see you. I love you, and 60,000 people at the Rose Bowl loved you too,” she remarked.

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