'Teen Mom 2' Sex Secret! Leah Messer & Married Ex-Husband Corey Simms Reportedly Got Busy In The Back Of His Truck

On this season of Teen Mom 2, troubled Leah Messer and her first ex-husband, Corey Simms, are constantly fighting over issues involving their 5-year-old twins, Ali and Aleeah.

But according to In Touch, a shocking new rumor is spreading around the former couple's West Virginia hometown: The 23-year-old mother of three and her married ex, 26, may have had sex!

"Leah recently had sex with Corey in the back of his work truck," a source tells the magazine. "She was just supposed to meet with him to talk about their daughters, not have sex!"

Of course, an illicit tryst would have serious consequences for both parents. As RadarOnline.com exclusively reported, Messer is dating and now living with personal trainer T.R. Dues, 32, while Simms is married to pregnant wife Miranda.

"He's admitted the affair to Miranda," the insider reveals. "It's a huge mess and all their friends know about it."

Another source tells In Touch that Simms vehemently denies sleeping with Messer, whom he recently called a bad mom on their MTV reality show.