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Paris Hilton's boyfriend Doug Reinhardt got into a fight with a man who tried to grope the heiress at a Los Angeles club Monday.

The two were dancing at H-Wood when an intoxicated male clubgoer approached Hilton and tried to touch her cleavage, a witness tells Usmagazine.com.

"Doug protected his lady and pushed the guy," adds another source. "That's when all of Doug's boys stepped in and beat the crap out of the guy. Then Doug had security kick him out of the club."

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Fellow clubgoers Jessica Alba and Cash Warren - who were dancing alongside Hilton and Reinhardt - were shocked.

"Alba and Cash looked at one another and were like, 'Wow,'" says an onlooker.

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(Despite several witnesses, Reinhardt's rep tells Us, "Doug was not involved in a fight last night.")

Hilton and Reinhardt didn't seem bothered by the brawl. They mingled with Brody Jenner around 1:20 a.m. before calling it a night shortly after 2 a.m.

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"They are very much in love and happy," a source tells Us of the two.

"They make the perfect couple. [They] are taking the family jet and headed to Kentucky for the Derby this weekend."

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Hilton confirms their weekend plans.

"I'm really excited to go to the derby," she tells Us exclusively. "This is my first time going and I love horses."