The husband of a missing Utah mom blew up his home Sunday —apparently intentionally — killing himself and the couple’s two young sons, authorities said.

Josh Powell’s house in Graham, Wash., exploded and burst into flames moments after a social worker brought the two boys Charlie, 7, and Braden, 5, for a visit with their dad.

Powell was under investigation in the disappearance of his wife, Susan, from their West Valley City, Utah, home in December 2009.

He claimed that she vanished mysteriously after he left to take the two boys camping — leaving after midnight in freezing weather.

The kids were living with Susan Powell’s parents, and a judge ruled Wednesday that Josh Powell couldn’t get them back without undergoing a psycho-sexual evaluation.

A social worker brought the boys to Powell’s house Sunday for a supervised visit, and Powell let them in but blocked the social worker from entering.

The social worker called her boss to say she smelled gas, and moments later the house exploded, according to Graham Fire and Rescue Chief Gary Franz.

Sgt. Ed Troyer, spokesman for the Pierce County Sheriff, said emails Powell sent to authorities suggest he planned the explosion.

And Jeffrey Bassett, Powell’s lawyer in his child custody case, said he received an ominous email from him minutes before the blast.

“I’m sorry, goodbye,” the email read.

“It’s the most horrifying thing you can imagine happening,” said lawyer Steve Downing, who represented Susan Powell’s parents, Chuck and Judy Cox, in the custody fight. “The Coxes are absolutely devastated. They were always very fearful of him doing something like this, and he did it.”

Kirk Graves, who is married to Josh Powell’s sister, Jennifer, said he and his wife believe the explosion was deliberate.

“His world was falling apart around him and he was going to lose his boys and get arrested for Susan’s disappearance,” he said. “He’s a narcissist and he has no love for anyone but himself

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