The Fenty Beauty founder attended the final show of Mariah's Christmas Time Tour at Barclays Center in Brooklyn Dec. 17 with boyfriend A$AP Rocky and Jason Lee. The trio stood on the floor for the show, during which Rihanna was spotted singing along to "We Belong Together," as well as "All I Want for Christmas Is You" and "My All."
Later in the concert, the "Umbrella" singer, 36, and the Hollywood Unlocked founder moved up to the front row, where Mariah noticed Rihanna while climbing a set of stairs onto the stage.
"Is that her?" the "Heartbreaker" singer asked. "Oh my gosh!"
In another angle of the moment, Rihanna took off her sunglasses and waved her hands, beckoning Mariah over, "It's me! I want an autograph!"
So, instead of continuing her ascent back to the stage, Mariah reversed course and walked backwards down the stairs to greet her.
"Doing this while walking backwards is a niche feat," she joked to the crowd. "I don't ever want someone to say I'm a diva again!"
Meanwhile, as she walked over to Rihanna, the "S&M" singer told Jason's camera that "my man told me to do this" before he reiterated that "Rocky made us do this."
The singer was visibly excited and asked her friend, "Should I have her sign my shirt or my t-t?" to which he suggested the latter.
"I need a signature!" Rihanna asked as Mariah approached. "Who has a Sharpie?"
"Who has the shades? Can I buy 'em?" the "Always Be My Baby" singer asked back, to which Rihanna replied, "Yeah, you can have them for free."
(Photo by Christopher Polk/NBC via Getty Images)
After receiving a marker from someone, Rihanna pulled down her shirt and Mariah asked the Savage X Fenty founder what she wanted her to write on her.
"'Mariah,' the f--k you think?" she joked. "Whatever you want. Wow, this is iconic!"
As the Glitter actress inscribed her signature on Rihanna's chest, the singer grabbed the mic from her other hand and addressed the cheering audience, saying, "Mariah Carey is signing my t-t, y'all! This s--t is f--king epic. Look at that s--t! Look at that s--t, y'all! I love you."
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The two singers them embraced as Mariah returned to the stage and Rihanna walked back to A$AP Rocky—with whom she shares sons RZA, 2, and Riot, 16 months—and gave him a big hug when she got back to their original seats.
Rihanna isn't the only surprise guest that has appeared during Mariah's holiday tour. Their viral moment together came one week after Mariah's 13-year-old twins Moroccan and Monroe—who she shares with ex Nick Cannon—surprised her with flowers onstage in celebration of "All I Want for Christmas Is You" returning to No. 1 on the Billboard Hot 100.
"Thank you. Wow!” Mariah said at her Dec. 9 show in Raleigh, North Carolina. "That was the perfect moment to find that out. It's from the Hot 100? Well, thank you, everybody who helped make that possible. Thank you so much."
And since it’s the season, keep reading for more secrets behind Mariah’s hit "All I Want for Christmas Is You."