Justin Bieber is close friends with the Kardashian clan, including Scott Disick's ex-girlfriend, Kourtney Kardashian. So, it's not surprising to see the singer hanging out with the mother-of-three and the rest of her sisters. However, the self-proclaimed Lord is reportedly not happy with Bieber after learning that the latter hooked up with Kourtney.

Disick is said to be shocked after learning of Bieber and Kourtney's hook ups. The 32-year-old has reportedly been working hard to patch things up with his ex-girlfriend, but realized it may be a little difficult now to win her back because of the Canadian pop star.

"Scott is trying to get better, trying to turn a new leaf and now Kourtney is going out late night and hooking up with another bad boy in Justin. So, Scott feels like it is a slap to the face. He feels that he is doing what she wants and she is now doing things just to make him feel bad," a source told Hollywood Life.

The source added that Disick feels like Kourtney is testing him by hooking up with Bieber. However, he only feels frustrated and thinks his ex-girlfriend is being "very hypocritical."

The source's claims came after Bieber allegedly bragged to his friends that he has been hooking up with the reality TV star. Another insider told US Weekly that Kourtney and the singer's hook ups have been happening for some time now.

"Every time Kourtney and Justin are together they're extremely flirtatious. They text each other all the time," the source said.

The pair has been spotted hanging out several times following Kourtney's split with Disick in July. They were spotted together on Friday, Dec. 11, at The Nice Guy, after which they headed off to Blind Dragon for some karaoke night. An eyewitness told the publication that Bieber and Kourtney seemed flirty with each other at The Nice Guy, where they were seen being touchy with each other and laughing together.

The 21-year-old "Sorry" singer and the "Keeping Up With The Kardashians" star first grabbed the dating headlines in October after they were spotted hanging out together at The Nice Guy. Although they spent dinner with different people, Bieber and Kardashian stirred rumors of romance when the reality star was spotted getting inside the singer's car after dinner. Amid the ongoing speculations, they continued to spend more time together afterwards. They were seen dining out at The Nice Guy again and even enjoyed a fun-filled night at the Universal Studios.