Brad Pitt is so big of a Frank Ocean fan ... he co-starred Saturday night in the singer's set at FYF Fest.
This video's pretty cool ... as Frank launched into his version of "Never Can Say Goodbye" by the Jackson 5, Brad appeared in the giant video screens. It looked like a pre-recorded clip of him listening to the performance on a phone ... although, he might have been listening live.
At the end of the song, Frank says, "This is for our good friend."
Brad's recently called out Frank's music ... saying it's helped him cope through the break-up with Angelina Jolie.