Kendall Jenner has now been romantically linked to half-sister Kourtney Kardashian's longtime boyfriend and the father of her three children, Scott Disick. And now, sources are reporting they know how the alleged affair began. 

According to OK! Magazine, via HollywoodLife.com, the model actually got caught on cameras flirting with her older sibling's boyfriend on the Kim Kardashian wedding episode of "Keeping Up with the Kardashians," which was filmed back in May 2014.

However, the pair's flirtation never made it on-air, and the hectic day allegedly gave Disick the chance to seduce Jenner. 

"Scott timed it perfectly," the publication claimed. "Everyone was so caught up in Kim's wedding that they didn't pick up on anything else that was going on around them, and Scott jumped at the opportunity to get cozy with Kendall."

The publication added that the two hooked up months later while in Europe, with Disick convincing Jenner that "there was nothing wrong with them misbehaving a little" since they are not related.

Star Magazine recently reported that Disick drunkenly proposed to Jenner.

"He didn't get down on one knee or produce a ring, but he said, 'We should get married,'" an insider revealed.

However, the 19-year-old allegedly shot her brother-in-law's proposal down, telling him to "end 'whatever this is'" and "go home to Kourtney and make things work."

Khloé Kardashian reportedly got furious.

"She hadn't realized things had gotten so out of hand between them," another insider told Star Magazine, via HollywoodLife.com, adding that she warned Jenner to "back off and distance herself" from Disick.

According to HollywoodLife.com, Kourtney, who is aware of the affair, is allegedly using her kids against Disick.

"Kourtney made it clear that if she finds out he's messing around with her little sister -- or anyone, really -- he'll never see his kids again!"