Jon Gosselin Cheating Scandal Heats Up!

Explosive new details have emerged about embattled reality star Jon Gosselin and his alleged affair with a 23-year-old schoolteacher!

Us Weekly has revealed new pictures that show the so-called other woman, Deanna Hummel, sunbathing in the Gosselin's front yard while wife Kate was away -- and a video of Jon leaving his alleged mistress' house at 7:30 AM.

"They've apparently been seeing each other pretty frequently," Jill Martin from Us Weekly tells "Extra." The magazine also chatted with Deanna's brother Jason -- who went into graphic details about Jon's overnight visits.

Jason, who lives with Deanna, reveals that Jon and Deanna "pretty much stay locked away...like two teenagers. It was weird. He's a grown man."

The other woman's brother also adds, "A lot of the time, it was pretty, um, gross listening to her, you know, um -- how do I say this? The walls are thin. Let's just say that. I mean, no one wants to hear his sister having sex, let alone with a married dude who's, like, almost twice her age and who has eight kids and a maybe-crazy wife. Ick."

Both Hummel and Gosselin vehemently deny the claims of a romance -- and Deanna tells People magazine that she's sickened by her brother's story. "My brother is making this all up. He has no credibility... I can't even stomach the lies he's saying about me."

Deanna suggests that her brother is trying to retaliate after she gave him the boot from their home. "He wanted to get back at me... he knows he's getting kicked out of the house."