WATCH: Tammy Daybell’s sister tells Dateline she was shocked and betrayed learning Chad had remarried

REXBURG — In her first television interview, Tammy Daybell’s sister is sharing how she learned her brother-in-law, Chad Daybell, had married Lori Vallow weeks after Tammy’s death.

Samantha Gwilliam and her husband, Jason, are speaking exclusively with Dateline NBC during a two-hour special Friday night. Gwilliam tells Keith Morrison that Chad told her Tammy had “been sick and had a coughing fit and passed away,” adding that Chad “sounded upset and devastated. I mean, I was crying and he was crying. It was a really hard moment.”

Chad married Lori Vallow in Hawaii less than a month after Tammy’s death. The Gwilliams had never met Lori and were stunned at the news.

“I was shocked because at that point, Tammy had only been gone for a month. And I just thought, ‘Is the grief clouding his judgment? I mean, who goes and does that? It didn’t make sense to me. And obviously, I was really upset,” Gwilliam says. “I felt like that was too soon for anybody to get over my sister.”

The new Dateline NBC will reveal new details on Tammy’s death and the passing of Lori’s former husband Joe. Morrison also speaks with mental health experts who say the deaths of the children could have been avoided if a court had listened to them more than a decade ago.

Dateline NBC will air Friday at 8 p.m. on KPVI Newschannel 6.

You can get the very latest details on the Daybell case here.