Throughout his relationship with Kourtney Kardashian, Scott Disick was frequently unfaithful.

But now, it seems the Lord is having anxiety over the possibility that his lady was stepping out on him toward the end of their time together.

Insiders have noticed that Scott is closer with his older two children than with his youngest son, Reign–and there are some interesting theories as to why that might be,

“This sounds horrible to say, but Scott is closest to Mason and then Penelope,” one insider tells Life & Style.

The source notes that while Scott has a bond with Reign, “it’s not the same as the one he had with Mason when he was that young.”

Part of the problem could be that Scott simply isn’t as involved in the life of his youngest child.

Though he’s always been an unrepentant partier, Scott assumed the role of attentive father when Mason was born.

He put on his dad hat again when Penelope entered the world.

With Reign, however, the circumstances were very different.

It wasn’t long after the birth of Scott and Kourtney’s third child that their relationship fell apart.

Scott and Kourtney split for good in 2015, when Reign was just six months old.

Shortly thereafter, Scott embarked on an epic bender, traveling the world in the company of increasingly younger starlets.

These days Disick is dating Sofia Richie, and his relationship reportedly takes up the bulk of his time.

So there are many factors playing into why Scott might not be as close with his youngest kid.

But insiders say the biggest reason is that Disick has doubts about whether Reign is really his son.

“Reign was conceived when Kourtney and Scott were going through a rough patch. At the time, Scott didn’t question whether he was the father, but that soon changed,” explains the source.

“It didn’t take long for Scott to start having doubts as to whether Reign is actually his child.”

The source adds that Disick became deeply concerned in response remarks made by family and friends:

“What really got under Scott’s skin is when family members said that Reign didn’t look like him,” says the insider.

“Penelope and Mason are dead ringers for Scott, but Reign looks more like Kourtney.”

The insider says that in the months before Reign was conceived, Scott and Kourtney often spent long stretches of time apart.

“There were countless times when they’d split up and not see each other for weeks. And whenever they had a huge argument,” says the source.

The informant claims that during that time, Kourtney often “went out of her way to seek revenge. She’d often party with her pals and close guy friends.” 

Scott has reportedly addressed these concerns with Kourtney, but it seems she refuses to acknowledge his suspicions.

“Kourtney didn’t want to hear it when Scott asked if he’s really the father,” says the insider.

“She outright denied [that Reign could be someone else’s],” the source adds.

“During the heated bust-up, Scott brought up doing a DNA test. Kourtney said no, which has only heightened his suspicions.”

So it seems the matter will remain a mystery–unless, of course, Kris Jenner can talk Kourtney into doing a DNA test for TV ratings.