Robert Pattinson and Kristen Stewart partied with Katy Perry

The 'Twilight' couple - who reunited on Tuesday night after a two-month separation while Robert was filming in Australia - joined a close-knit group of friends to help celebrate Katy's assistant's birthday on Wednesday evening.

In a blurry six second video posted on YouTube, Kristen - who is good friends with the birthday girl, Tamra Natisin - can be seen standing next to Robert and appears to be taking a phone snapshot of him, while Katy brings out a cake and initiates a chorus of 'Happy Birthday'.

The 'Part Of Me' singer seemed in a good mood considering she has just split with boyfriend John Mayer after a seven month romance.

Kristen and Robert - who briefly split last summer after she was caught cheating with married film director Rupert Sanders - have been making the most of their time together by hitting the town for nights out.
News of the pair's reunion was made public on Tuesday at a karaoke bar in Los Angeles, and a lucky fan managed to get a photo with the pair.

Fan Laura Austin tweeted: "I just ran into them at a karaoke bar by my house... mellow night. They were just there hanging out with a few friends."