Paris Hilton and Doug Reinhardt split because she violently attacked him.
The heiress reportedly lost her temper when she arrived at Los Angeles club Darkroom to find her boyfriend talking to a scantily-clad blonde earlier this week.
An onlooker told E! Online: "Paris decided to drop by while Doug was on a boy's night out, but when she got there, she found him looking very cosy with a half-naked blonde girl.
"Paris turned into a raving lunatic. She threw a handful of limes at the girl, before shoving her up against a wall. She then started scratching and hitting Doug.
"He called her a 'f***ing crazy b***h' and she stopped. Doug's friend hightailed it out of there and Paris and Doug left together a short time later."
However, Paris' spokesman has denied she was involved in a bar fight, claiming the relationship ended when Paris realised Doug was a "publicity hound" who was only dating her to get famous.
In response, Doug issued a statement saying: "Doug refuses to take part of this ridiculous media circus. He wishes Paris and all of her future boyfriends the best of luck."
A friend of Doug's has claimed Paris is desperate to reunite with 'The Hills' star, saying: "Contrary to reports, Paris is begging him to take her back. She made a mistake and loves him 100 per cent."
However, Paris doesn't appear to be missing Doug too much.
The 28-year-old socialite was seen kissing soccer star Cristiano Ronaldo on Wednesday night (10.06.09), less than 24 hours after she split from Doug.
The pair left Los Angeles club MyHouse together at 3am, driving straight to sister Nicky Hilton's nearby house in West Hollywood.
Cristiano - who is moving from English team Manchester United to Spanish club Real Madrid in a reported Â£80 million transfer - was videoed leaving the mansion at 5am with a cheeky smile on his face.