AceShowbiz - Gigi Hadid may be best friends with Kendall Jenner, but it doesn't mean she will approve of her making out with Anwar Hadid. Words are, the 23-year-old model is worried that the "Keeping Up with the Kardashians" star will break her brother's heart.

"Gigi is giving her little brother a warning," a source close to Gigi tells HollywoodLife.com. "She told him that Kendall is a heartbreaker, and not to fall in love with her. Gigi knows that Kendall puts work and her career first with little time for a serious boyfriend or a long term relationship."

She allegedly doesn't want her brother to get his hopes up, especially because he "has had a crush on Kendall for years." The source notes, "Gigi fears her younger brother will fall in love with Kendall after one kiss so she told him to slow down." The blonde beauty also makes it clear to Anwar that "while Kendall is a beautiful, sweet, smart, sexy and a trusted friend, she is not to be messed with."

While Gigi appears to oppose the idea of them dating, Kylie Jenner has given them her approval. The mother-of-one is reportedly "hoping that Kendall will finally settle down" not that she is with "someone as awesome as Anwar."

"Kylie knows Anwar is good people and is really hoping Kendall will give him a real chance," another source tells the site. "Kylie's way ahead of herself, but she's already talking about how gorgeous Kendall and Anwar's babies would look, they'd be supermodels for sure. Kylie's so happy and in love with Travis [Travis Scott (II)] and she wants her sister to have the same thing. She's so pro-relationship and can't understand why Kendall is still single. She's hoping Anwar will fix that."

Kendall was caught on camera engaging in a hot makeout session with Anwar at a CFDA Awards after-party at Socialista New York. According to onlookers, the pair were together at the bash for about two hours, "kissing, cuddling and drinking."