The 26-year-old singer gushed Tuesday on Twitter after singing "No More Tears (Enough is Enough)" with Streisand at the 77-year-old recording artist's concert at United Center.
"hello shaking and crying. thank u @BarbraStreisand. don't have words yet goodbye," she wrote.
Grande followed up by posting a photo of herself with Streisand.
"cherishing this moment forever @BarbraStreisand," she wrote.
Grande also gushed about the experience on Instagram Stories, calling it "the best night of my life."
Streisand shared a color version of the photo with Grande on her own account.
"Secret's out. Thank you @ArianaGrande," she wrote, adding three heart emojis.
Sources told People the audience at United Center "went wild" and gave a standing ovation after Grande and Streisand performed "No More Tears (Enough is Enough)," a 1979 duet Streisand originally recorded with Donna Summer.
"The entire theater turned into a dance party immediately," a source said. "The whole place got up."
Streisand had teased a collaboration with Grande Monday by posting a photo of just their hands.
"Made a new friend," she wrote.
Grande had her own concert Sunday in Chicago and will kick off the European leg of her Sweetener world tour Aug. 17 in London. She released the new single "Boyfriend" last week.
Streisand will next perform her Simply Streisand show Aug. 23 in Milton, Del. She last released the album Walls in November, which includes the single "Don't Lie to Me."