X17 EXCLUSIVE DETAILS – Lindsay Lohan, Katy Perry And A Porn Star ... Oh My!

We haven't seen Lindsay Lohan and Katy Perry party together before, but we're lovin' it! Throw in James Deen, the porn star ... and we're talkin' a sexy threesome. Deen will be starring with Linds in the upcoming flick, The Canyons.

The 26-year-old redhead hit the Shore Bar to celebrate the 4th with the "Firework" singer. Lilo, as usual, gave good face to the cameras on her way out, but Katy ... not so much. Even though she was dressed in red, white and blue from head to toe, Russell Brands' ex tried to stay under the radar.

Perry had performed in New York earlier in the night ... even hiring strippers for the NYC bash. But after a quick 5-hour flight, she finished up the holiday at the Santa Monica bar.

As for Lilo, her porn buddy picked her up at 2:30am, and the two headed to the Casa Del Mar hotel for some after-hours fun.

Perhaps Linds saw some fireworks, afterall!