JENNIFER ANISTON and KIM KARDASHIAN are tangling over one of Hollywood’s hottest hair­dressers.

Jen’s longtime stylist and close pal Chris McMillan – the genius behind her famous “Rachel” ’do from “Friends” – has trimmed his quality time with her to become BFFs with Kim because he feels the raven-haired beauty is not only nicer but a bigger star too.

“Jen is stewing,” disclosed an in­sider. “Of all the men in her life, Chris has been the one constant. He stood by Jen through her marriage and breakup to Brad Pitt and all of her love-life ups and downs.

“Jen expected he'd always be loyal. Now she’s furious – at both Chris and Kim – for the betrayal.”

Kim, 32, posted pictures of Chris working his magic on her locks on the so­cial networking site Instagram on Dec. 18, with the caption: “fun shoot today.”

“Jen was fuming when she saw the photos because she and Chris used to watch ‘Keeping Up with the Kardashians’ together and mock the family,” continued the insider. “Jen sent a message to Kim to back off, but Kim isn’t scared of her. And the plan actually backfired – Chris was furious at Jen about it.”

According to the insider, Chris feels that Jen turned her back on her longtime friends after hooking up with fiancé Justin Theroux, and things only got worse when the couple got engaged in August.

“Chris feels edged out by Justin, who he says makes Jen’s old friends uncomfortable by talking down to them,” noted the insider.

While Jen, 43, and Chris remain cordial and have no plans to dis­continue their partnership in their hair-care line, Living Proof, the friend­ship has been damaged.

“Chris is raving about how fun-loving and sweet Kim is,” added the insider. “He says she’s a real breath of fresh air after having to constantly hear about Jen’s body insecurities and relation­ship traumas. Chris now likes hanging out with Kim much more than Jen.”