Brad Pitt Shows Up to Jen Aniston's 50th Birthday Party

Brad Pitt just arrived at Jennifer Aniston's birthday party ... this is not a drill.

The former husband and wife reunited Saturday night at the Sunset Tower Hotel for Aniston's star-studded birthday bash.

Pitt arrived solo in a black Escalade and quickly made his way inside, trying to dodge the photogs who were already buzzing about the big event.

The stars, who were married from 2000 - 2005, have been back on speaking terms for quite some time. As we reported, they sparked a friendship back up as Pitt was splitting from Angelina Jolie, but nothing romantic had developed between the ex-lovers.

The "Friends" star has been very open in discussing her marriage to Pitt, recently describing the relationship as "successful," despite a divorce.

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Pitt and Aniston won't be partying alone, as many of her Hollywood friends have also arrived, including Katy Perry, Orlando Bloom, Gwyneth Paltrow, Jason Bateman, Jennifer Meyer, Reese Witherspoon and Ellen DeGeneres. Orlando and Perry arrived via motorcycle ... so cool.

DeGeneres had previously floated the idea of throwing Aniston, who turns 50 on Monday, a party on her daytime show.

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As we reported, Aniston isn't the only ex Pitt has met with recently, as he reunited with Angelina Jolie in Beverly Hills to discuss their ongoing divorce.

The two were scheduled to continue private discussions regarding the custody of their six children, and were seen during tense negotiations. Afterwards, Jolie left for work in Bangladesh while Pitt stayed in L.A.

Meeting up with this ex-spouse will hopefully be a much more relaxed situation for Pitt.

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