This was a once-in-a-lifetime event. Ariana Grande joined Barbra Streisand during her concert in Chicago on Tuesday.

The surprised United Center crowd saw the two performers sing Streisand’s classic  No More Tears (Enough Is Enough). The audience gave them a standing ovation. After the show, both Grande and Streisand posted pictures together on Instagram. What legendary act would you like to see perform a duet with a star from today?

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