This undated photo provided by the Duke Marine Robotics and Remote Sensing Lab shows two humpback whales in the Antarctic.

PROVINCETOWN, Mass. — A commercial lobster diver was seriously injured Friday morning when he was caught in the mouth of a humpback whale off the coast of Cape Cod, his sister said.

Michael Packard, 56, of Wellfleet, was taken to Cape Cod Hospital with at least one broken leg, his sister, Cynthia Packard, told the Cape Cod Times.

“He was swallowed by the whale, he was in his mouth for about 20 seconds,” she told the newspaper in a phone interview.

Cynthia Packard got details of the encounter off of Provincetown from her brother’s crewmate, who at first feared it was a great white shark.

Charles “Stormy” Mayo, a senior scientist and whale expert at the Center for Coastal Studies in Provincetown, told the newspaper that such human-whale encounters are rare.

Humpbacks are not aggressive and Mayo thinks it was an accidental encounter while the whale was feeding on fish, likely sand lance.