Susan Powell's father-in-law says he had secret sexual relationship with the missing Utah mom

The bitter family feud over a missing Utah mom took a tu for the creepy when her father-in-law claimed they shared a flirtatious relationship replete with "sexual touching."

The revelation infuriated the missing woman's dad, who blistered Steven Powell and his salacious comments as "outrageous, cowardly and despicable."

Steven Powell, appearing Thursday on ABC's "Good Moing America," said he kept the sexual shenanigans with daughter-in-law Susan a secret from her husband, Josh.

"It was pretty much not something that really came to light," Powell said. "We interacted in a lot of sexual ways because Susan enjoys doing that."

Susan Powell was 28 years old when she disappeared on Dec. 6, 2009, from her family's Utah home. Husband Josh told investigators that on the night she vanished, he was camping with his two sons - ages 2 and 4 - in the middle of a blizzard.

Susan's father, Chuck Cox, lashed out at the comments made by Steven Powell regarding his daughter.

"I see these attacks as outrageous, cowardly, despicable and not believable in any way," Cox declared on NBC's "Today."

"I trust that the media and the public can see right through this," Cox said. "Basically, he's trying to blame the victim, and my daughter is the victim here."

Cox made it clear that he finds Josh Powell's camping trip tale is bogus.

"I'm suggesting the story he's giving is not believable, not credible, has not basis in fact," Cox said. "If he's innocent, he should go talk [to police] and clear up these issues so we can go on with the business of finding my daughter."

The network television war of harsh words followed a Tuesday court hearing where a Washington state judge ordered Cox and Josh Powell to stay 500 feet away from each other.

Powell had claimed that Cox was stalking him - even showing up at a home improvement store to mouth the words, "You're dead."

Cox denied the allegations, and his lawyer insisted that he only wanted to hug his two grandsons.

Last weekend, the two families engaged in a screaming fight as reporters watched outside a local grocery store.