EXCLUSIVE: More 'Bachelorette' Drama— Kaitlyn Bristowe Caught With Nicole Richie's Hubs, Joel Madden

At the Imagine Ball, a charity event held at L.A.'s House of Blues on June 4, Kaitlyn Bristowe made a beeline for none other than Joel Madden, who is very much a married man—and the father of two, with wife Nicole Richie.

"There wasn't any buzz beforehand that Kaitlyn would be attending," says a source. "It seemed that she wanted to go as incognite as possible almost as if getting her hooks into Joel was her main mission of the night."

After Joel and his twin brother Benji performed as the gala's headline act, the brothers moved to a VIP area, where Kaitlyn would soon follow. "She caught his eye and he strolled over to say hello, then they shared a big hug," says the eyewitness.

"Kaitlyn was being superflirty, reaching out to touch his arm as they chatted," the insider tells Star exclusively. "They clearly had a lot of chemistry."

And it doesn't help that the Good Charlotte rocker Joel and Nicole, who have been married four years, have been fighting like crazy. "She's controlling and moody, and he's tired of it."

"Nicole hates that he acts like a single man when he parties at events," the source claims. "She knows what he's like when he drinks and doesn't trust him. She's constantly checking up on him, and that only makes him want to act out more."

And Joel isn't exactly the type to turn an attractive fan away. As a source puts it: "Female attention is a bonus."

"Kaitlyn has a rep of being a real party girl in her native Canada," says a behind-the-scenes source on The Bachelorette. "A fling with a married rock star wouldn't be a stretch for her." But Joel had to part for some meet-and-greet duties, and Kaitlyn wasn't too thrilled about that. "I wouldn't be shocked if she gave him her numbers," the eyewitness says, "or even if they made plans to meet up later."

Get more on this story—pick up the new Star issue that hit newsstands June 17!