Justin Bieber and Kourtney Kardashian are rumored to be "casually hooking up" after she was recently spotted leaving his residence well into the early hours of the morning.

According to Gossip Cop, the much older 36-year-old "Keeping Up With The Kardashians" reality TV star was spied leaving the 21-year-old Bieber's Beverly Hills abode around 4 a.m. Saturday, following a night of hanging out together.

The evening started with friends at the L.A. hot-spot The Nice Guy. From there, the group headed for the Blind Dragon karaoke bar where the mother of three was seen leaving much earlier than the "Baby" crooner.

But their separation proved short lived, and soon enough Kardashian was spotted strutted from his hotel room decked out in all white.

The suspected rendezvous between the two isn't the first. Back in early October, they again chowed down at The Nice Guy and later posted pics of themselves on Instagram frolicking at Universal Studios.

Sources describe the dalliance between the two as not serious and insist the two are just having fun.

After more than nine years and three kids together, Kardashian and longtime boyfriend Scott Disick split earlier this summer after he was spotted openly cavorting with ex-girlfriend Chloe Bartoli in Monaco over the July 4, holiday weekend.

Since then, Disick has also been romantically linked to teenage model Lindsay Vrckovnik.

Eventually, Disick spent 30 days in a Malibu rehab facility and is currently rumored to still be receiving outpatient treatment. More recently, he and Kardashian have also been spending much more time together with their three children and have been rumored to be trying to iron out the issues in their relationship.

Meanwhile, Bieber is rumored to be single, though he was recently spied serenading on-again, off-again girlfriend Selena Gomez.