The Oscar-winning actress finds herself embroiled in yet another love triangle.

Reese Witherspoon has warned Jennifer Aniston to keep her hands off her man after Jen and Jake Gyllenhaal shared a passionate kiss at a recent awards ceremony in LA.

Presenter Jake left the audience stunned when he swept up the 38-year-old actress in an intimate embrace and locked lips as he presented her with an award.

"It wasn't just a polite peck on the cheek. There was definitely feeling in that embrace," says one witness.

Reese, who is filing for divorce from Ryan Phillippe, broke down in tears after hearing about the kiss.

"Why would he do that?" she despairingly asked a close friend. "Why would she do that?"

"Reese is very unhappy about it because she really thinks Jake is everything that Ryan wasn't," reveals the shocked friend. "She thinks he's sensitive, caring and understanding. Now she's beginning to wonder …

"She always thought Jake to be intelligent and charming. That's why she's so stunned by the photographs of Jake and Jen. She's really hurt by what she's seen. They seem to be very explicit and everyone knows Jennifer's looking for love."

Just days earlier, Reese and Jake had agreed to make their romance official after months of speculation they were a couple.

While Jake, 26, is a good deal younger than Jen, it's not the first time the pair have been romantically linked.

The two set tongues wagging when they cosied up on the red carpet after playing lovers in The Good Girl in 2002, and were also spotted having several intimate dates in the months following Jen's divorce from Brad Pitt.

They have also talked openly about their fondness for each other, leaving many to speculate that they're more than just friends.

"I like to think I'm his Mrs Robinson," Jen once joked, while Jake says, "I like her, honestly. Everyone falls in love with Jennifer."

Friends say Jake is now working hard to win back Reese's trust.

"She's the most exciting woman I've met in years. She's beautiful, intelligent, she's a family woman, a fantastic mom and someone who knows what true love is," he gushed to friends.

"If I've made her mad, I'm sorry. I mean really sorry. She's the best thing that's happened to me. I have so much respect for her, and I think we are falling in love. I wouldn't do anything to hurt her intentionally. I should have been more careful."

For the full story see this week's issue of Woman's Day (on-sale April 23).