Katy Perry may have reunited with her former flame, John Mayer the other day, but she planned a secret rendezvous with Robert Pattinson Saturday night!

The two spent time together at Santa Barbara's Santa Ysidro Ranch a week and a half ago and hung out in New York a few weeks before that -- in fact their relationship was said to be the reason Rob and Kristen Stewart broke up.

On Saturday night, Katy and Rob were back together, as they hit up the Bjork concert at the Hollywood Palladium.

They arrived separately at 7:30pm, but met up before heading inside. Our photographer on the scene tells us:

    "They had planned to meet up before going inside to the concert. They must have been coordination on their cells phones because they pulled up next to each other in the parking lot, rolled down the windows and were talking. They parked and then met at the door and went inside together."

They stayed together throughout the show but tried not to be seen together when they left. Our photographer tells us:

    "Katy came out the back door by herself, trying not to be noticed. She was looking around to see if there were any photographers. She definitely didn't want to be shot with Rob."

So will Katy and Rob become official? Or will Katy get back together with John Mayer? Or will she pull double duty and choose them both? :)