The 'Beautiful' hitmaker paid a visit to the tourist-heavy Rockefeller Center concourse earlier this week, and stopped by the popular coffee shop much to other customers' surprise, reported E!Online.
"There were only about 10 people in the store at first, but when people started to realise who she was more and more (people) came in. She took a lot of time to take pictures with the customers," an onlooker said.
Aguilera, 34, also took to Twitter and posted a photo of herself autographing a paper cup, and added the caption, "Coffee on me for the next hour! Head to 30 Rock (30 Rockefeller Plaza)! Xo Xtina (sic).