Blake Shelton better watch out! Funny guy and talk show host Jimmy Fallon impersonated the singer, performing 'I'd Want It to Be You' with Barbra Streisand, and she was pretty impressed.

The gorgeous Streisand appeared on 'The Tonight Show' to talk about her new duet-based album 'Partners' and perform. But one thing was missing: a duet partner. Said Fallon, "She's got duets with legends like Elvis Presley, she does a duet with Blake Shelton, Michael Buble. So, of course, Elvis is no longer with us -- spoiler alert -- Blake's over at 'The Voice,' Buble's on tour, so instead, standing in for Elvis, Blake and Buble will be ... me."

At this, the audience cheered and by the impish look on Fallon's face, he had a few surprises up his suit coat sleeve. Instead of simply singing a medley of songs with Streisand, he donned outfits and personalities to match those of the three missing men, and the effect was hilarious.

When the medley came to 'I'd Want It to Be You,' the song Streisand and Shelton recorded, Fallon grabbed a black cowboy hat and uncovered his country boy side.

Fallon surprised Streisand, because after a rather wincing Elvis impersonation, he carried a tune well, definitely doing the song justice. "I can hardly tell the difference!" Streisand exclaimed during the song, and after his Shelton impression, stated, "That was actually good!" with a look of disbelief.

Of course, no one could ever replace the ultra-talented country star Shelton, but at least Fallon has the same wit and humor the 'Neon Light' singer possesses, making for a highly entertaining evening on 'The Tonight Show' set.

Shelton's new album,'Bringing Back the Sunshine,' drops at the end of September.

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