Rumors say Scott Disick believes Kourtney Kardashian cheated on him and is questioning if her last child, infant Reign, is actually his.

A source tells OK! exclusively Disick has been "acting strangely" for a while, which can explain why he has been spotted with his older children Penelope and Mason but never out with Reign.

"Scott's not the only one who was up to no good," an insider says. "She's definitely acting as though Reign is hers, not theirs. It's just a really sad situation for everyone."

Back in 2013, model Michael Girgenti said he slept with Kardashian while she was on a break with Disick stating that he is the real father to Mason. Yet, the "KUWTK" star has shot down those rumors giving proof that they were false.

Are these just rumors?

Disick has been publicly accused of cheating on the mother of his children and was spotted cozying up to his ex-girlfriend over the summer causing their recent breakup. He has also never completely trusted Kardashian after the cheating rumors.

Yet, it has been reported that Disick and Khloe Kardashian's ex-husband Lamar Odom may write a book about all the dark secrets about the "Keeping Up With the Kardashians" clan.

"There has been plenty of offers made to both Scott and Lamar to write a scandalous tell all," a source revealed. "If they decided to work together for one juicy book it would expose a lot of the Kardashains' dark secrets."

Will Disick reveal that Kourtney has actually cheated on him? Or is it just rumors and speculation?

Meanwhile, E! News reports that Disick wants to get back with Kourtney while she has no interest in him. Yahoo! News also reported Disick no longer has access to the house he and Kourtney used to live in together.

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