Once spotted, Maxwell — who was sitting alone with a pet pooch — told an onlooker: “Well, I guess this is the last time I’ll be eating here!”

A source told The Post that a daily regular took the photo.

“He’s at In-N-Out every single day,” the source said. “He went up to her and asked, ‘Are you who I think you are?’ She replied, ‘Yes, I am.’”

Maxwell was reading a book called “The Book of Honor: The Secret Lives and Deaths of CIA Operatives” and seemed resigned to having her picture snapped, the source said.