Mayor Bill de Blasio had a brief exchange in Italian with Pope Francis before Thursday night's service at St. Patrick's Cathedral -- seemingly catching the pontiff off guard with his language choice.

De Blasio said Friday morning on the "The Joe Piscopo Show" on AM-970 The Answer that he greeted the pope by saying, "Benvenuto, Santo Padre," which translates as "Welcome, Holy Father."

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The mayor said the pope responded by asking how someone who spoke Italian became mayor of a great city like New York.

See alsoComplete coverageInteractiveYour messages to the popeSee alsoPope's visit: Follow along at News 12

The mayor replied that New York was a city of immigrants, and the pope's voice was the most important in the world for immigrants.

De Blasio said in another radio interview that Francis is "inspiring."

"He is such a warm person, such a kind person," de Blasio said in an interview on WCBS 880. "You can tell in just a few words, this is extraordinary person."