BRITNEY SPEARS is trapped in a love triangle that is turning violent.

She’s involved with ex-boyfriend Justin Timberlake and rocker Fred Durst, lead singer of Limp Bizkit — and jealous Fred, who’s no stranger to violence, is threatening to teach Justin a lesson, say sources.

“Fred says that if Justin doesn’t back off, he’s going to kick his boy-band butt,” revealed an insider.

The short-fused rocker once beat up a man who has having an affair with his wife. He later was arrested and served a month in jail.

Now a pal of Justin warns, “Fred’s told friends that Justin better not cross his path. He looks at Justin like he’s a pushover.”

Britney fell in love with Fred while also rekindling her feelings for Justin, say sources.

“Britney had a plan that backfired on her,” revealed the insider.

“She wanted to make Justin jealous hoping he’d come back to her and would want to see her exclusively. She used Fred Durst to make Justin jealous — but then she fell for Fred after starting to hang out with him about a month ago.

“Fred loves to listen to Britney when she talks about her feelings and her dreams. That’s something Justin never did.

“Britney had suggested to Fred that they go to some of the local clubs in L.A., knowing they were the same ones Justin and his pals frequent.

“Britney knew word would get back to Justin — and she was right!

“Justin called Britney one night and asked her about Fred. Britney told him she was helping Fred with some lyrics and they were just friends. She told him Fred was a sweetheart — but there was nothing between them.

“But Britney and Fred were falling in love.

“Justin took what she said at face value, but Fred started to question Britney.

“He heard reports of Britney and Justin getting back together and asked her to explain what was happening.

“Britney told Fred she and Justin were just friends and that if they bump into each other while out and talk a minute, or if they got together over a few drinks, it’s simply to catch up on what’s new in their lives.

“Britney told Fred he was the man she wanted to be with and he openly shared his feelings with her, too.”

The two recently went to the trendy Nacional club in Hollywood, where they sat in a cozy booth holding hands.

“Justin was at the same club with his buddies,” disclosed the source. “After Britney saw Justin looking at her, she and Fred slipped out a side door.”

A smitten Durst even posted his feelings toward Britney on the group’s Web site:

“Anybody who has a serious problem with my feelings for Britney should just chill… I have never felt this way. I really like her and I’m happy to know her right now.”

Revealed the insider: “Even though Fred has made his feelings for Britney public for the world to see, it has’t stopped her from still wanting to be with Justin. In December, Britney and Justin were seen at her Manhattan apartment kissing and hugging in the elevator.

“Then after the recent ‘American Music Awards,’ she was seen kissing and holding hands with Justin.”

Now the pop princess is being torn by the very tug-of-love she created.

“When Britney’s with Fred, she’s sure he’s the man she should be with,” disclosed the insider.

“But when she’s with Justin, her feelings for Fred switch off and she’s certain that he’s the man for her.

“She needs to make a choice.”

Meanwhile, Justin had better avoid fuming Fred, said Timberlake’s pal.

“Word has filtered down to Justin through mutual acquaintances that Fred wants Justin to stay out of his face!”