Jef Holm on Brother's Cheating Allegations: What The ...

Jef Holm says he has no idea why his brother would accuse Emily Maynard of cheating on him and insists, adamantly, that The Bachelorette couple is fine.

Earlier this week, Us broke the "story" that Emily was sexting behind Jef's back, and that their family vacation ended early and tumultuously as a result.

The couple quickly denied the tabloid cover story, only to learn that the source of the report was Jef's brother Mike Holm ... who stood by it a second time.

That has Jef in disbelief - and denying it all over again.

"My family all says they are shocked, and obviously I'm shocked," Jef says of Mike, who vacationed with the Holms, Maynard and her daughter last weekend. But, he adds, if everybody knew the history he had with our family, no one would be surprised."

An emotional Jef Holm and Emily Maynard slammed the story, again.

"This whole story is 100 percent false," he reiterates.

"I like to give Mike the benefit of the doubt and think he's changed, but obviously he hasn't. He has a history of doing hurtful things to the family," says Jef.

After the cheating reports first surfaced, "I called every single member of my family and asked them if they'd said anything, and he promised he hadn't."

"He's been cut off from a lot of family things because he's so dishonest. It's so disturbing to think that a family member would do this."

Even so, he adds, "as hurt as I am, I love him and I love my family."

If there were trouble in paradise, Jef's putting on one heck of a good front. He's been Tweeting up a storm about how much he loves Emily Maynard.

Not only that, he's been gushing about little Ricki, going to school with her and even meeting Emily's late fiance's parents, "the nicest people ever."

Safe to say the lovebirds are on steady ground and then some.

Emily Maynard and Jef Holm: Will it last?