Family members recall in a TV documentary Thursday night how they learned of the cancer that had struck NBC special correspondent Tom Brokaw.

"I didn't believe you!" Brokaw's wife, Meredith, says in a preview clip for the "Dateline" episode "Tom Brokaw: A Lucky Life Interrupted," in which the former "NBC Nightly News" anchor interviews her. "I mean, that's something that you just out of the blue cannot absorb in one take," she tells him. "I didn't panic. I didn't think, 'Oh, this is the end of the world.' I just needed to know more. Because I really didn't understand what we were dealing with."

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Sarah, one of the couple's three children, tells Brokaw, 75, that she began to realize the extent of his multiple myeloma one day at the family home in Montana, where "you were having a lot of back pain. And you had asked to get a kiss from [grandson] Archer. And we leaned down to give you a kiss. And your body just convulsed. You just -- your body became paralyzed. And I thought, 'Something is seriously, seriously wrong.' I think it was such a pivotal moment for all of us. All of a sudden recognizing that no, life is so finite and you might be gone."

Brokaw said in September that he is in remission from the cancer that he announced publicly in February 2014.

Multiple myeloma is a form of cancer affecting blood cells in the bone marrow. Doctors consider the disease incurable but treatable, with experts saying new therapies have rendered it a chronic disease.