Joe Jonas was a surprise guest performer at his fellow U.S. pop star Billy Joel's London concert Friday.

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Both artists posted photos from the show on their Instagram accounts after singing Joel's classic song, "Uptown Girl," together.

Joel's account said: "Special Guest Star @joejonas joins Billy Joel at@bsthydepark. LONDON."

Jonas shared a video of the duet.

"This still feels unreal. Thank you to my friend @billyjoel for having me on stage to sing 'Uptown Girl' with you tonight in Hyde Park. You've been a big inspiration to me and this was a bucket list moment. Life made," the younger singer wrote alongside of the clip.