Mayor de Blasio will undergo surgery Friday for a hernia that “developed recently,” his office said.

Recovery time will be quick, with the mayor back at City Hall Monday, his spokesperson Karen Hinton said Thursday.

The cause of the hernia is unclear.

Hinton said that it isn’t related to the 54-year-old mayor’s exercise routine — and that it occurred in “the line of duty.”

She didn’t offer any more details.

De Blasio regularly travels from Gracie Mansion to his old neighborhood in Park Slope to work out at the local YMCA.

If the mayor was in pain Thursday, he didn’t show it.

Hizzoner was all smiles during a nearly two-hour ceremony at the Intrepid Museum in Hell’s Kitchen, where he signed a bill into law establishing a new Department of Veterans’ Services.