After it was reported that Kourtney Kardashian is hooking up with family friend Justin Bieber, a new report claims that the mother-of-three, 36, is denying anything happened with the Biebs, 21 — which has the singer laughing because he knows the (alleged) ~truth~.

Sources tell TMZ that despite the Keeping Up With the Kardashians star’s denial, the two are very much some sort of item and first began seeing each other in October when they ran into each other at a club in LA.

RELATED: Khloé Kardashian Has a Pregnancy Scare — Get the Details

Since then, they have allegedly seen each other on several occasions — including, most recently, a 4 a.m. hotel rendezvous in LA this weekend.

Kourtney is reportedly insisting she hasn’t hooked up with her younger sister Kendall Jenner’s rumored sloppy seconds — but a source tells TMZ she’s lying to herself, though noting their relationship is far from serious.

RELATED: Kim Kardashian and Kanye West Are Told Baby No. 2 Should Be Their Last: Details

“He’s single, she’s single and they’re just having a good time,” the source says. “Nothing serious.”

When it comes to their romance, JB’s lips are sealed as well — though he did upload a cryptic, steamy Instagram picture, captioned, “Lord knows,” which may have to been a not-so-subtle nod to Kourt’s baby daddy and ex, “Lord” Scott Disick.

For access to all our exclusive celebrity videos and interviews – Subscribe on YouTube!