L-R: Brandon Davis, Doug Reinhardt and Paris Hilton (WENN.COM file photo)

Paris Hilton's 29th birthday party was thrown into chaos when her boyfriend Doug Reinhardt got into a fight with her pal Brandon Davis.

Onlookers were stunned after the heiress and former The Hills star Reinhardt began arguing in the middle of New York hot spot Tea Room on Thursday (18Feb10).

A furious Hilton walked off, and moments later Reinhardt was at the centre of another screaming match with oil heir Brandon Davis, who was once romantically linked to the socialite.

Reinhardt was said to have been angry after Davis arrived unexpectedly and appeared to be inebriated, according to The New York Post.

A source tells the publication, "One minute, Paris and Doug were looking all loved up; the next minute, they started bickering. Doug didn't seem happy about all the attention she was getting. Paris started to pout and gave him some girly punches in the back before storming off.

"The next minute, Doug was shouting at Brandon. The music was so loud that we couldn't hear what he was saying, but he then got Brandon thrown out of the door."

But the birthday girl patched things up with her boyfriend and ended the night with a smile on her face.

The insider adds, "She and Doug were looking all romantic by the end of the night."