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Credit: Rogelio V. Solis/AP

Call it First Lady’s night!

Michelle Obama and a female friend dined at Giuliana and Bill Rancic’s restaurant, RPM Italian, in Chicago on Wednesday night.

As she entered the front door of the bustling River North restaurant, the First Lady – who was dressed in all black – received applause from the surprised room of diners, an onlooker tells PEOPLE.

“She waved to her fellow Chicagoans before entering a private dining room,” the source adds.

After their 90-minute meal, the First Lady stopped to thank Chef Doug Psaltis, adding that she hoped the restaurant would soon open a location in Washington, D.C., soon.

The First Lady is in the Windy City to celebrate the three year anniversary of Let’s Move, her anti-obesity program.

– Jennifer Garcia