No wonder she's always walking around with that smug look on her face these days!

Kourtney Kardashian hit the studio to film scenes for Keeping Up with the Kardashians yesterday and then spent the rest of the day hanging with her kids, and we think it's nice that she took the afternoon to be a mom, because lately all she seems to be doing is boning Justin Bieber!

Rumors that the reality star and the pop star were having sex surfaced back in October, but then they sort of died down until recently, when People reported that the pair are still quietly doing the deed whenever he's in town. "They have hooked up a few times, including recently. It happens in L.A. He has met her kids, but they don't hook up around the kids. It's on nights when she has help and is able to go out," a source dished to the mag.

"Kourtney is great. Justin thinks it's cool that she is older and hot. She isn't clingy and has her own life. There are no bad consequences for Justin to hook up with her. She is very easy going and just makes it fun for him to be around her," the source added.

The mother-of-three clearly has no self respect. Not only did she turn a blind eye to Scott Disick's cheating for years, but now she's OK with sleeping with The Biebs even though she knows he's banging a handful of other b*tches!