Just call it a sister act: Judging by all their cuddly selfies, you’d think Amelia and Delilah Hamlin are thick as thieves. But behind the scenes, the girls are anything but chummy, an insider tells OK!

“They’ve been competing with each other for years, and now that they both have celeb boyfriends, they’re convinced the other is trying to hog the spotlight,” spills the insider. Ever since Amelia, 18, hooked up with Scott Disick, 37, last fall, Delilah’s “annoyed because her sister’s getting way more attention than she is,” dishes the insider, noting that the blonde beauty, 22, has been dating Love Island’s Eyal Booker, 25, for more than two years. 

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Meanwhile, Disick and Hamlin have been together for around three months — from the time they were spotted together at a Halloween party. And now, their romance seems to be getting serious — as OK! previously reported, the two are smitten with each other, and Hamlin is “so different” from anyone Disick has ever been with.

“Scott does everything he can to make Amelia happy,” the insider noted, adding that Hamlin is beautiful, funny and self-confident, and Disick really finds it irresistible.