You can disguise Christina Aguilera, but you can't disguise her voice.

The "Accelerate" singer went incognito with Jimmy Fallon on The Tonight Show Thursday, busking in a New York City subway station. "No one knows that this is going to happen," Fallon teased. "Nobody knows that it's Christina Aguilera. Let's do this!" As they covered Aretha Franklin's "Think," passersby on the 47-50 Street Rockefeller Center platform took notice of Aguilera's unmistakable vocals and filmed the surprise performance on their phones. The duo then removed their not-so-glam disguises. "It's so it in here!" Aguilera said. "Oh, my God!" The jig was up, so Aguilera and Fallon gave the fans what they wanted: a performance of "Fighter!"

(In previous Tonight Show episodes, Miley Cyrus, Maroon 5 and U2 busked with Fallon.)

Aguilera appeared on the program to promote her new album Liberation, out now. After she turned the PJ Masks theme song into a lullaby and discussed her return to the spotlight, the singer treated the audience to a solo performance of "Fall in Line," her duet with Demi Lovato.

On Friday, Aguilera performed as part of the Citi Concert Series on Today.

(E! and NBC are both members of the NBCUniversal family.)

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