Scott Disick and Kendall Jenner reportedly had a sexual relationship when Kourtney Kardashian was pregnant with their third child.

According to HollywoodLife.com, Star magazine claimed that the "Keeping Up with the Kardashians" stars have been getting quite close with each other. Apparently, Disick's ex-girlfriend Kourtney Kardashian has been uncomfortable with the way that the then 31-year-old was "always checking out" her then 19-year-old half-sister.

The publication went on to reveal that Scott Disick and Kendall Jenner have been having a "steamy affair" behind Kourtney's back. It was said that the pair had sex at a party and a mutual friend was able to tell Kourtney about it.

"After their partying episodes, he saw Kendall as an adult," a source said. "A superhot and fun one at that."

"This is what their relationship has turned into. What should be a brotherly/sisterly love has become sexualized. Scott clearly finds her attractive, and she likes the attention. It's just wrong."

It was noted that Kourtney Kardashian was understandably horrified and angry at the discovery. "At first, Kourtney was in complete shock and disbelief," the insider added.

"But after she processed the information, she was devastated ... She started screaming at [Scott], calling him 'sick.' But he kept denying it. He stormed out and the next she heard of him, he was doing what he always does - drinking his problems away. This time it wasn't in Las Vegas, it was in Aspen."

It was previously reported that Scott Disick and Kendall Jenner sparked speculations on their relationship as they were caught getting cozy recently. The "KUWTK" stars got a little too close for comfort as they waited for their ride outside Nobu Malibu after they celebrated Rob Kardashian's birthday.

A video showed Scott Disick and Kendall Jenner talking with their faces really close. They were surrounded by several people.

A scene in the clip showed the 20-year-old supermodel putting her arms around the self-proclaimed lord. A worried Scott also leaned on the door and appeared to make sure that Kendall was okay as she climb on the front seat of a car which Kourtney was driving.