INSIDE the heartbreaking tragedy gripping the nation in an exclusive ENQUIRER special investigation!

The family of missing Utah mother Susan Powell is devastated knowing they’ll likely never find out what happened to the beloved mom after the only suspect in her presumed murder – husband Josh – killed himself and their kids on Feb. 5. What’s more, The ENQUIRER has learned that Susan’s oldest son, 7-year-old Charlie, told his grandparents he didn’t want to see his father for the court-ordered visitation that fateful day.

As it turned out, Charlie andhis younger brother Braden, 5, died in a raging fire their father deliberately ig­nited after they arrived at his rented home in Graham, Wash.

“It’s still not real to me,” Susan’s shattered sister Denise Cox told The ENQUIRER in an exclusive in­terview. “I’m in shock. Josh took my sister and then he took my nephews. It was a cowardly thing to do. He has caused so much pain to my family.

“My mom and dad were raising those kids, and now they’re crushed.”

In December 2009, Susan Powell, then 28, went miss­ing from her West Valley City, Utah, home. Josh told police he had taken their sons camping in the desert in freezing tempera­tures in the middle of the night, and that Susan was gone when they re­turned home in the late afternoon.

But Susan’s family members have long suspected she was killed and her body dumped somewhere in the desert. Now they fear she’ll never be found.

“Josh left that family in tortured agony,” said a friend. “The location of Susan’s corpse died with him.”

Several family members have speculated that Josh was in a state of panic because his children had re­cently become more vocal about what happened the night their mother disappeared, even sharing that she was “in the trunk” of the car.

Police believe that Char­lie may innocently have let slip his newly verbalized memories to his father.

“They think maybe Charlie said something to Josh that let him know his wicked game was coming to an end,” said the source.

On Feb. 1, Josh lost a battle to regain custody of the boys from their grandparents. He was given visita­tion rights. But on Feb. 5, little Char­lie resisted visiting Josh when a social worker came to take Braden and him for the scheduled visit.

“No! I don’t want to go see Daddy,” he told his grandparents.

Said the friend: “Charlie was upset. He made it plain he didn’t want to see his dad.”

When the social worker finally ar­rived at Josh’s home with the boys, Josh pulled his young sons inside and slammed the door in the social worker’s face. Within minutes, the house exploded and was engulfed in flames. Josh, Charlie and Braden all perished.

“The family is in agony imagining what Josh said to Charlie and Braden before he set off the explosion and the terrors they went through in their last moments,” the source said.

Denise added: “We knew he was capable of doing something. We just didn’t realize it would be something THAT horrible.”