Former President George W. Bush paid an unannounced visit to the 9/11 museum Sunday evening, and spent an hour somberly looking at the exhibits.

“He was clearly moved by the museum and its contents,’’ said a law-enforcement source.

Bush arrived at 6 p.m. with his security detail while the museum was still open to the public.

Some people recognized him, but were respectful of his privacy and did not try to approach him.

He did shake hands with some Port Authority police officers at the museum.

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