Olivia Rodrigo makes surprise appearance at Billy Joel's MSG show

At his 82nd monthly concert in his Madison Square Garden residency Wednesday night, Billy Joel welcomed the latest of his occasional onstage guest stars: Olivia Rodrigo, the 19-year-old singer-songwriter whose string of multiplatinum hits includes "Deja Vu” — which gives a shout-out to Joel and his song "Uptown Girl."

"I'm going to bring up another young musician," Joel, 73, seated at his revolving piano, told the sold-out crowd, according to an audience video posted by a Variety magazine writer. "This is a very talented singer-songwriter. She's a triple Grammy winner" for best new artist, best pop vocal album ("Sour") and best pop solo performance ("Drivers License"). After listing some of her awards, Joel added, "She's very talented, and I like her music and so do my kids. Please say hello to Olivia Rodrigo!"

A beaming Rodrigo walked onstage in an earth-toned miniskirt with strata pattern, a black, sleeveless corset top and calf-length, lace-up, black leather boots. She waved to the crowd — "Hey, guys!" — then turned to Joel to thank him for having her as a guest. "I'm such a huge fan. I've kind of written this next song about you."

As the audience roared upon recognizing the tune, Rodrigo performed "Deja Vu," last year's upbeat ballad in which the narrator excoriates an ex-boyfriend for doing the same things with his new love that he used to do with her. Among the narrator's complaints: "I bet that she knows Billy Joel / 'Cause you played her 'Uptown Girl' / You're singin' it together," even though "I was the one who taught you Billy Joel."

When the song ended, Hicksville-raised Rock & Roll Hall of Famer Joel, in his trademark dark suit, black shirt and tie, got up from his piano and hugged Rodrigo. He then told the crowd, "We're going to do a song that was referred to in the last song." To yet another roar, they sang together on "Uptown Girl" and hugged again afterward.

"Thank you, Billy, I love you!" Rodrigo told him, and then skipped offstage.

"I sang with Billy Joel at Madison Square Garden today are U kidding," she posted afterward with a photo at Instagram Stories, where posts cycle out after 24 hours. In a second photo, showing the two onstage smiling with their arms around each other, she posted a heart emoji. Then on a closeup shot of the two together backstage, she wrote, "Biggest honor ever still crying thank u Billy!!!!!!!" Rodrigo also posted a snippet of her "Deja Vu" performance and a photo of the two onstage taken by an audience member.

Joel's social-media team as well posted images and video footage of the two onstage and backstage.