Hailey Warns Newly Single Kourtney K.: Stay Away From My Man!

Cougar Kourtney Kardashian is single — and Justin Bieber's fiancée Hailey Baldwin is worried she'll come calling for her ex, RadarOnline.com can exclusively report.

Two weeks after the mom of three, 39, split from longtime boyfriend Younes Bendjima, 25, she's ready "to go after Justin in a heartbeat, if she had the opportunity," a source told RadarOnline.com.

As RadarOnline.com readers know, Bieber, 24, and much-older Kardashian dated from 2016 into the following year.

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"Things between Justin and Kourtney were more serious than most people realized," the source insisted. "Their physical compatibility was off the charts, and they even started to bond about religion. Justin was hugely attracted to Kourtney, and she was really smitten by him. They had a lot of fun together."

The pair split, and Bieber went on to date Selena Gomez, 26, and then current fiancée Baldwin, 21.

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But Baldwin isn't so secure with her quickie engagement, the source claimed.

"Hailey is very protective of her relationship and she has every reason to feel threatened," the source continued. "She's saying that Kourtney better stay away from Justin, and she won't hesitate to ban him from speaking to her altogether."

As RadarOnline.com previously reported, Baldwin is also insecure about Bieber's longtime romance with ex Gomez.